To much cam??

Your combo is out of wack. The easy fix is swap to a smaller cam. A very adjustable distributor would be good.

My buddy did this in a '79 Ram Charger with the same exact results.
For some stupid reason, he refuses to change the cam. I've told him to change it like Um-teen times. His excuses are lame and stands by them. He makes no sense. The engine was built for a super charge with that same cam.

"The cam is where all the engines balls are at.... Right?!"
"I want a lump lump lump idle! And that's final!"
The guy that built it is a MoPar guy and said it would work in my truck!"

After the Um-teenth time, I just said yea it is your right of course how stupid of me!