I had the same problems on a 1972 D-jet.
After replacing all vacuum lines, fuel lines, points, rotor, condensor, cap, wires, and plugs......

I kept having a poor running engine, plus the problem changed each time...meaning it would run ok with the #3 injector unplugged, then next time it was #2 etc...

I replaced all the injectors, checked grounds etc... I even did a test with all the injectors squirting into bottles, turning over the engine for 20 seconds and measuring the fuel...

Finally I pulled the distributor out and took a good look inside at the vaccuum advance mechanism.
It had 30 year old grease that was hard and caked on there, and when I took it off the car it was really hot,I mean really hot, too hot to touch...

so I took the distributor apart, cleaned all the parts and re-assembled using new grease... Approx $0.02 worth
Car runs perfect...
It really was hard to diagnose, but remember the car is 30 years old and sometimes the problem is just old age....

Rich

you can make an inexpensive fuel pressure tester. i got a pressure gauge 0-100 psi from home depot. it was found in the area where they have sump pumps (water pumps). it is a nice, big about 2" diameter gauge. then get a brass fitting(s) to be able to connect fuel line to the gauge, 2 worm gear clamps....
pressure is 35 connected, 28 unconnected (verify)