Well I happen to be one that does believe in big carbs as back in the day I picked up nearly 2/10ths on my stock bottom ended/stock 2.02 headed '71 340 with an 850DP over a 750DP, I ran a TA 4200stall and 4.30's. I doubt in your case it would make any difference, a 750 if worked proper can work just as well on a set up, one test for carb sizing is if you have zero vacuum on WOT its too small. I would definitely get a new converter and your issues probably will be solved hopefully.
