Don't give up on the Holley yet. I am assuming it has been throughly soaked and cleaned and blown out and all passages inspected to be clear. Suck on the idle tubes to be sure. Old crud is hard to get out.
Be sure there is a good seal between the carb body and the idle body. Snugged up. No sealers.
Start with idle screws out 1.5 turns. Increase .25 turn at a time for one more full turn. When you get it running hot, close up the idle screws .25 turn until it misses, the increase .25 turn.
Try closing the choke half way, even more. If it is lean, this will richen it. A good diagnostic check.
Check the float height. Try raising it. These are tiny increments. Remove the top after running gas into it and make sure the jets are fully covered. Even then raising it may help.
I would not think the low flow gravity feed would be a problem at idle and low speed, but maybe. You will need a pump anyway to drive it fast.
A faulty power valve installation will richen the mixture. I think you are running lean. Good luck. They will work.
