I have a 80's head with the 1.75 intake hole. The first carb I used was a 350 cfm off a 351 mod. Ford motor it was a big change. I also put a Mallory cd box and Ecoil on a few days later. The next day I did a 4500rpm 1st to 2nd shift and just about put it in the ditch, that carb swap made a big differance. Now I'm running a 350 cfm Demon carb, I also swapped my rear end fron a 2.79 gear to a 3.45, which made my mpgs go up even more. Now I'm getting about 20 city and about 22-24 on the hiway.
The biggest problem I've had is my Demon carb sweats very bad on cold wet days, I ported out my adaptor to give it as steep of incline towards the middle as I could so water wouldn't gather and make big drops. I also put the thinnest gaskets I could find in order to make the carb get as hot as possible, and ran my pvc hose to the carb instead of the factory location on the carb adaptor.
I'm not sure how every one else has their carb tuned but I had to go up 2 sizes on the acc.pump squirter and I changed out the main jet from a size 60 to a size 64 on the Demon carb, I would think the Holley carb would be close to the same.
Hope this helps, Daniel