Back to the carb question:
The debate on here regarding AFB v Holley will never end. Indeed, two of the members whose opinions I regard highly (Feets and Mr yuck) have differing opinions for you.
I went through a few Holleys before switching to an AFB. The AFB trumped the Holleys, but for one simple reason: I bought a strip/'calibration' kit and learned to tune it. I never did anything to the Holleys other than twist the idle screws.
That said, I've since put a 1050 dominator on my 505". Bought the Quickfuel metering blocks and spent a little time tuning it up. It's now awesome on the street.
While dropping the 750 on for the race day might be the simplest/best short term solution, buy a tuning kit for the AFB and go nuts...
It's all to common on here to read about someone who's new carb is 'junk' out of the box (goes for both brands/styles), all because they never spent any time tuning it.
Got a buddy how used to have an Aussie 6-pack hemi. That guy would literally spend hours tuning those carbs, at idle, with fancy mercury filled tubes. That thing was always a rich running pig at anything off idle. Could never get through to him that he needed to play with the jets, or whatever those weber carbs had.
Anyway, enough of my rambling, tune that sucker before shelving it.