I have a 72 Chevelle 454. The previous owner had the engine re-built. He said it has a mild cam and roller rockers, headers and a 3” exhaust, Edelbrock intake and carb. All I did was install the drive train after the restoration was complete. It’s a monster. Runs great at over 1500rpm + - but it misses at idle and when initially coming up to speed and it also backfires thru the exhaust when decelerating. My area is in the body and paint etc portion of the restoration and some mechanics. I know nothing about tuning these. Does anyone have any ideas how to correct this?