Classic/Antique Car Repair: 1965 chev ss, impala ss, two different things

Question
I bought a 65 impala ss with a 327, it had only been driven about 50 miles in the 3 yrs. I drove it home and had trouble with backfiring, stopped and got anew battery that solved that problem. We kept going and had some more backfiring, had trouble keeping it running at stops. Got home   and changed plugs cap rotor points & condenser, the car will start and idle great but when you put it in gear and start to move it will backfire and not have power. I had a mechanic adjust the carb but didnt help other advice was to check rocker arms and pushrods but dont see anything wrong there so now i'm stumped. Could it possibly be the qjet carb?

Answer
There are two different things that people call "backfire" and I need to know which you mean.  Tell me if there is actually fire coming up out of the carburetor when this happens, or do you mean that there is a loud bang from the exhaust system?

Post a "follow up" question back to me with your answer to that, and maybe I can give you some advice.

Dick