Original pre-'98 F-series bed bolts are carriage-type, with long square or oval bosses under the heads. Even if they don't spin during removal, they often break due to rust. New replacements are not available (as of the upload date), but newer-style bolts CAN be made to fit with almost no modification.
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This bolt spun, so I welded a temporary grip to the head. After removal, I removed the grip, and welded splines under the head so it couldn't spin again. But it's a lot of work, and requires even more damage to the bed, so it's not a good solution.
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Don't forget to remove any OTHER bolts holding the bed down, before attempting to lift it off. But to make this swap, the bed barely needs to be lifted - just one side at a time, and just a half inch is enough.

These aftermarket bolt kits are affordable, and good enough, with 8mm Allen (hex recess) heads. At least 2 short and at least 2 long bolts of at least 6 bolts total are required; the other 2 can be either length. But some short bolts are not threaded as far up, so look for those with a noticeably shorter unthreaded shank. Genuine Ford bolts are much more expensive (new, but common & nearly free in JYs), but higher quality with T50 heads. Genuine nuts are 1-piece, and threaded properly.
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Aftermarket long bolt dimensions in mm.
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Aftermarket nuts included with bed bolts are crimped too much. If they're simply installed, they'll spin in their U-clips. To prevent that, chase each one with a lubricated bolt (anti-seize is what I use) before installation. Note that the vise is gripping the socket which holds the NUT - not the U-clip.
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I sometimes use this portable gantry (made from scrap metal: a 5" Aluminum I-beam, some 1.5" straight square tubes, and some 2" square tube T's, with common 5/8" hitch pins to adjust the height) with a 12V ATV winch for outdoor lifting. It could have even been powered by the truck's own battery, but I wanted to be able to set the bed down and drive the truck without it. To lift pickup beds, I use a common 2x4 cut slightly longer than the width of the bed under the lip (so it can't spin in the bed) with a heavy screw eye in the center. A few test-lifts to find the balance point take less than a minute before it can be lifted high.
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Lifting the bed this high is NOT necessary simply to swap bolts. But this truck was getting a lot of other work done.

After thoroughly washing the frame (and whatever repairs prompted removing the bed are completed & checked), install the later-style U-nuts (chased with anti-seize) on the frame so the bed is easier to remove next time.
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The hole over the axle needs to be enlarged just this much for the later bolts to fit.
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Lifting the bed is easier than it sounds - it doesn't weigh much, and an empty one can be lifted by 2 strong adults. But a 12V ATV winch on a portable gantry is very convenient & relatively cheap, which is what the top left pic shows. A 110VAC winch costs about the same.
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If the bed is tilted as in the lower right pic, don't let it slide off the frame, or pry against the bumper. I chained the bed to the frame before tilting so it couldn't slide or shift. But to ONLY change the bolts, it doesn't need to be lifted as high as shown - that truck needed fuel tank work.

But it doesn't need to be lifted this high or tilted this much JUST to swap to the later-style bed bolts & U-nuts. These trucks were all getting MUCH more work done.

Undercoating the exposed threads will protect them from rust, without interfering with removal.
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The front Left bolt is hardest to see because of the front tank (if equipped).

'94 F150 Dimensions
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See also:
https://www.fordpro.com/en-us/upfit/publications/



Frame Service - Drilling Precautions

CAUTION: Do not drill holes in the frame flanges. This will reduce the strength of frame (5005).

If a hole must be drilled in the frame, make sure that it meets all of the following requirements:
1. The hole is located in the upper half of the frame.
2. The edge of the drilled hole and the edge of the nearest hole are at least 25mm (1 inch) apart.
3. The edge of the drilled hole is at least 25mm (1 inch) from the edge of the flange.
4. The drilled hole is not adjacent to any other existing brackets or components of frame.

Welding Precautions

CAUTION: Disconnect the battery ground cable (14301) before using any electric welding equipment.

All welding on frame must be done with electric welding equipment, and the heat should be kept in a small area to prevent change in hardness of the metal. Do not use gas welding equipment. A double reinforcement must be added to frames where heat or weld is applied to the area to be repaired. The welds are to run lengthwise along the reinforcement when a reinforcement is to be welded to the frame side rail.

Frame Strength Identification
F-Series, F-Super Duty Chassis Cab and Bronco all use a 36,000 psi steel frame.

Frame Straightening
Misalignment of frame can be corrected by straightening the out-of-line parts or by replacing the crossmembers, braces, or brackets if they are badly damaged.

WARNING: DO NOT STRAIGHTEN FRONT FRAME RAIL CONVOLUTES.
Straightening should be attempted on frames that fail to meet specifications of the diagonal checking method or where damage is visually apparent.

However, to prevent internal stresses in the metal, frame straightening should be limited to parts that are not severely bent. If heat is needed to straighten a frame member, keep the temperature below 649C (1200°F) (a dull red glow). Excessive heat may weaken the metal in the frame members and cause permanent damage.

Frame Reinforcing

After a bent frame member has been straightened, inspect the member closely for cracks. If any cracks show, the frame member should be reinforced or replaced.

Reinforcements should be made from angle or flat stock of the same material and thickness as the frame member being reinforced, and should extend a minimum of 152.40mm (6 inches) to either side of the crack. Ideally, the reinforcement should be cut from the corresponding area of a similar frame.

Weld Attachment

To ensure a quality repair, adhere to the following procedure if it is necessary to weld reinforcements to the frame.
1. Wire brush the area around the crack to remove the paint, grease, mud, etc., and to expose the crack completely and ensure good weld adhesion.
2. To stop the crack from spreading, drill a 6.35mm (1/4-inch) hole at a point 12mm (0.50 inch) beyond the root of the crack.
3. Grind out the full length of the crack to the hole to form a V-shaped slot with the base of the V-slot contacting the reinforcement.
4. The base of the V-slot should have at least a 1.52mm (0.06-inch) opening to ensure weld penetration to the reinforcement when welding the crack.
5. Drill clearance holes in the reinforcements to clear rivet heads and bolt heads or nuts where necessary.
6. In the event that repair is required on more than one frame surface (i.e., a flange crack that extends into the web), two pieces of flat stock (one for each surface) should be utilized and welded together where they join. The web reinforcement should be a minimum of 76.20mm (3.0 inches) high and have a 63.50mm (2.5-inch) radius at each of the two corners.
7. Completely clean the surface of frame under and around the reinforcements.
8. Clamp the reinforcements securely to the frame prior to welding.
9. Weld the reinforcement all around after welding the crack V-slot.
10. The flange edge weld should be ground smooth after all pit holes have been filled by the weld.
11. If a damaged bolted-on frame bracket is to be replaced, the new bolts, washers, and nuts should be of the same specifications and bolt torques as the original parts.
12. In cases where it is necessary to remove rivets, replace them with Property Class 9.8 metric (Grade 8 ) nuts, bolts and washers of the next larger size (i.e., for 3/8-inch diameter rivets use 7/16-inch bolts, for 7/16-inch diameter rivets use 1/2-inch bolts). This requires line drilling of the holes to the same diameter as the new bolt (i.e., either 0.437 diameter or 0.500 diameter).

Frame Member Replacement

If a damaged frame member is to be replaced, new bolts, Property Class 9.8 metric (Grade 8 ) fasteners and rivets required for replacement of parts should be of the same specifications as the original bolts or rivets. In cases where it is necessary to substitute a bolt for a rivet, use the next larger size bolt.