What is on it now? Like LS said, backfiring through the carb isn't always anything to do w/the carb- and certainly not because of the size- there are scads of 2-bbl 350's and bigger engines running fine.
Most likely, you need to tune the timing curve and perhaps adjust the carb, depending on what it is and where it was originally.
What is the current initial and total timing, and what is the vacuum at idle. Need that to go further on tuning it.
In the meantime, check for vacuum leaks, at the intake gaskets, the carb base, any/all vacuum hoses, PCV, etc.
Double check the plug wires- 1-8-4-3-6-5-7-2. Cylinder #1 is driver side, front. Alternates driver side to passenger side for #2, etc.