Chevrolet Repair: backfire problem, deg btdc, vacuum gauge

Question
Hi and good day to you. I have a 1973 c-10 with 350 4bbl carb. I just aquired this truck. Before I got it, it was converted to HEI igniton, has a new edelbrock carb with spacer plate, new cap, rotor and plugs. Looking in my haynes manual, it calls for R44T plugs, but they had installed R45TS plugs in it. Talking to a local parts store, they looked it up and said those plugs would work as well. The problem is no matter where the timing is set which is currently at 8 deg btdc, it backfires through the carb with the slightest touch of he accelerator. It starts up and idles like a dream, but due to backfire, we have adjusted the  carb lean to rich and everything in between, timing advanced and retarded and everything in between, but no results, still backfires through carb. also, did the old school manually setting timing at TDC and made cetain that rotor was pointing at #1 on cap, I cannot figure out what is wrong which is the first time in 30 years!!  Hope you can help me, and thank you for your time. hope to hear from you soon. Thanks again.

Answer
GOOD DAY TO YOU BOB,,,THE SPARK PLUGS THAT YOU HAVE IN THERE NOW IS JUST A LITTLE HOTTER PLUG THEN WHAT IT CALLS FOR...THIS IS OK..BACK FIRE THROUGH THE CARB COULD BE A IGNITION PROBLEM, WEAK SPARK LIKE POSS COIL FAILING. BUT THE OTHER THING THAT MAYBE HAPPENING IS A FLAT CAM LOBE NOT LETTING A VALVE OPEN..THIS WILL CAUSE A BACKFIRE UP THROUGH THE CARB. YOU SAY IT IDLES OK BUT CAN NOT REV IT UP. DO YOU HAVE A VACUUM GAUGE,IF SO SEE IF THE NEEDLE IS BOUNCING AROUND..IF IT IS I WOULD SUSPECT CAM OR VALVE PROBLEMS. YOU MAY NEED TO REMOAVE THE VALVE COVERS TO CK THIS.. TIMING CHAIN COULD BE WORN AS WELL. GET BACK TO ME AFTER YOU CHECKED THE ABOVE AND I WILL GO ON FROM THERE..TOM