I put in a new distributor, that came with points and condenser. That didn't get it. New coil, still didn't stop the popping. I did go 20 miles at 60 mph with no problems. today I finally drove and stopped three times to create the problem again. When I got home I popped the hood and revved the engine by hand. It would randomly pop. I started pulling plug wires from the distributor, and revving to get a pop, and reconnecting the wire. The engine didn't pop when I disconnected the fourth wire. I had the truck at the mechanics before this started. New manifold gaskets, and valve adjust. I suspect that some of the hydraulic lifters may have collapsed and only fully expand after the engine core temperature goes high enough, this could cause an intake vale to not seat fully. The mechanic suggested some '70's cams were notorious for developing low spots, that causes the exhaust valve to not open fully, leaving exhaust gasses to blow out when the intake valve opens. So now I could adjust the rocker, but I should check the lifters at least. What do you think?
