350sbc running ruff

Gotta 57 chevy wiv a 1973 350 sbc. Problem is i bought car as none runner.Got it started but it backfires big time. When i pull off front plug cap on drivers side(can anyone tell me cylinder numbers!?) engine continues to run the same but backfiring significantly cuts down.Got a good old shock off the lead,so's theres power there & its a new plug.Anyone help?

If your ignition timing is set properly, the next step is to inspect the timing chain. It may have stretched so much it has skipped a tooth, so your cam timing is off.