Axle Vent

The Chrysler ones have a valve in them, and terminate right on the axel.

IIRC the Ford's were just a barb fitting and the hose ran up into the frame rail, there might have been a valved fitting on it up in there ( it's been a long time)

Drill the bolt, tap it for a fitting, put on a barbed nipple, run the hose up to the frame rail, probably best to go to the passanger side drivers side might have the gas tank vent depending on year.