Rough idle on my 81

[WFBT2]

I'm having problems with the idle on my 81. I recently swapped the engine from my parts car and now with all the plug wires hooked up it will fire on only 2 cylinders but if I remove any of the plug wires it will rev higher and hit on 3. The dist. cap, rotor, plugs, wires, and magnetic pick up are all new. Also checked and cleaned as many grounds as I could find.
Any help would be greatly appreciated.

[spider2081]

Have you checked the static timing?
The temperature sensor in the coolant "T" causes crazy problems.
There are a couple grounds that connect to the drivers side cam box and one on the passenger side cam box. all are close to the firewall. Are they in place??

[WFBT2]

The timing is good, when it's running on 3 cylinders the timing mark is very close. I have 3 ground wires on the drivers cam box and 1 on the pass. side connected to the cover plate. The temp sensor is plugged in but I don't know what kind of shape it might be in. I've never had a car run better with 1 of the plug wires disconnected.

[spider2081]

Any chance you changed the timing belt and inadvertently swapped the car gears???