I have a 570 street avenger on my 68. It came with the car when it had a mild cam. I shoved a bigger cam in there and she still runs like a top. I love Holly carbs.

 

I can't comment to much on this forum from a mustang point of view (as I have an old Carter 4 barrel on mine), but I had an old 69 International pickup on the farm with a 460 that had dual 4150s on it. I had entirely to much power as I could spin all four tires with it locked in on dry pavement with just motor. I'm going back to Holly once I get a 351 for my stang.