[lha1992]

Dude your physically moving distributor is prolly just needing the timing adjustment/clamp down bolt tightened. Happens just look on the side of the dizzy at the base where it goes into the engine you'll find a clamp with a bolt keeping it from moving.

BTW don't worry about an alternator when the truck isn't even running correct like you said backfiring an what not. You'll beat yourself for buying a new alternator when you coulda used that money to fix the engine to run better. Fix one project at a time rather than go all over the place. It'll get outta hand seriously.