A few things to check/consider. Good luck.
1) Since you replaced the wires, cap, and rotor, just wondering if the plugs were replaced also. If so, check the heat range on the new plugs. Too hot a plug could cause both these problems ("pinging" & run on). If not replaced, check plugs for deposit build up and general condition.
2) Not familiar with the 76, but looks like you are mixing parts from different years. May want to check that the old and new rotors & caps are indexed the same (both point to the same terminal at the same time). If out of whack, this should only affect "pinging".
3) Again not familiar with the 76, but some carbs had a solenoid that would close the throttle when the ignition was turned off. This was to reduced run on. With all your activity in the area, maybe it was disturbed (if so equipped).
4) My 71 2000cc had a run on problem caused by bad valve seals. The extra oil would cause excessive deposits which acted like little glow plugs. Messed up one clutch disk trying to stop run on by putting it gear to stop it.