/6 wont Idle

So I finally got the '72 Dart running. It was my fathers and he had it sitting for 15 years, I got it to my house and switched over to electronic ignition because the points weren't working for me and the fact that I hate points.

Well it fired right up and sounds great, but I cant get it to idle right. I was thinking it was the 318 holley 2280 thats on it, but after talking with my father I'm not sure.

He was telling me that he could never get this motor to idle right (he's actually pretty good at these sorts of things). Another thing that caught my attention was that the original 1 barrel was better in every way. It had a 20 mph high top speed and got 6 mpg better than the 2 barrel.

So I am wondering if there is anything mechanical in the engine that wont let the engine idle right and have a loss in power/mpg?

If it helps any the current motor is supposedly out of a '76 valiant? But was a factory super six 2 barrel