Oh the dreaded edlebrock peformer flat spot, junk that carb and save yourself the headache of even thinking you can get it right.
I would recomend a Holley HP 650 double pumper unless your motor has allot of compression and cam your gonna want the smaller carb.
You'll get much better throttle response from a smaller carb than going to a bigger one like the 750. Also I would recomend a tad less plug gap than .055, somewhere between .035 and .040 is where you wanna be.
Goodluck, Charles