Footbrake cars can usually benefit from tuning the accellerator pump circuit. It can be squirting not enough initial volume(too small of a squirter), not long enough (too small of a pump cam), too much initially or for too long. A bigger squirter will reduce the duration of the squirt a bit because it dumps it all faster. Test at the same temps and launch rpms because that can make some difference in the results. There are some good books on Holleys that could help and have pump cam info outlining the sizes and profiles of the pump cams. It could also help to get both front and rear squirters to finish squirting at about the same time. Squirting for too long can be as bad as a bog from not long enough because the engine goes into an over-rich condition, then has to recover.
Tune the pump cam & squirters for 60' and jets for MPH.