Not too familiar with that engine but sounds like something in the distributor is amiss.

Since you've not yet checked for spark at the plugs that's your first and most important step. Seems to me I've read more than a few posts about the electronic ignition module, either inside the distributor housing or mounted externally that is most often a reason for your condition.

Also sounds like a thorough tune up with new plugs, cap, rotor, wires etc etc is in order too.

FWIW there is another sub-forum here that deals with your era engine---I know the guys and gals there would be very helpful. Try this: https://www.ford-trucks.com/forums/forum53/

Hope to see some photos of your freebie sometime soon!