I recently revived a 302 that had been parked for 14 years. I did not want to
pull the pan so found the following on a web site:
Assuming you can turn the engine through by hand.
1) Pull the plugs - I shot PB Blaster down each cylinder
2) Drain the oil and replace drain plug
3) Remove the dip stick and then rig you a funnel on the
dip stick tube so you can introduce liquids directly into
the oil pan
4) Pour 3 quarts of Zylene through the funnel, down the
dip stick tube into the oil pan
5) Let this sit for a couple of hours or more.
6) Drain the Zylene from the oil pan
7) Pour 3 quarts of kerosene down the tube into the
oil pan.

Let this sit for a couple of hours
9) Drain the kerosene
10) Remove the funnel and replace the dip stick
11) Remove the old oil filter and replace with one of your choice
11) Add required # of quarts of oil - should be 5 on a 351
At this point you need to make sure the gas tank hasn't been
fouled. Mine had old gas in it. Had to have our local radiator
shop clean and seal. You should also clean the fuel line from
the tank to the carb. Take it loose on both ends and shoot some
brake cleaner fluid through it. Complete the job with your air
gun. If it has an inline filter - replace it with a new
one. If it doesn't have one, I suggest you add one.
Add new plugs, battery, fresh gas and give her a go. Assume it
starts (and a FORD) always does, it will smoke like all get out.
This should subside over time.
I suggest you run the engine for about 20 minutes. Shut it down
and remove the oil filter. Toss it out (I know you just put it one
a half hour ago but it will have collected a lot of residue that was left
in the pan) and replace it with a new one. Top off your oil
and good luck.
Hope this helps.