I'm not sure this is the knob that will stay here, but it works & looks OK. The hole for the knob only affects the (previously UNused) small switch plate, and I'll probably add something to the other side soon (like a digital pyro gauge).
Regardless of this switch, the high idle is DISabled if the brake lights are on, or if the shifter is in any gear other than P or N. This truck idles at 730 RPM (off); low is 1070; medium is 1360; hi is 1600.
It's POSSIBLE that this switch is equivalent, but I haven't confirmed that:

{-Clickit