Classic/Antique Car Repair: 1963 buick lesabre timing chain diagnosis, distributor shaft, stock distributor

Question
car runs like a crossed plug wire exhuast very rich & sputters at tail pipe. new carb,plugs,plug wires,pointless ignition.fresh fuel. compresion 160 all 8,fuel pressure 5 lbs, fireing order good,spark to all 8,no vacume leaks or pluged exhuast. runs smoother at higher rpm but still back fires thru carb when wide open throtle.timeing at 12deg before 401cid v-8 4 barrel carb carter AFB 78,000 origanal miles please help me diagnose thank you   william r bluhm

Answer
I am not a fan of aftermarket pointless ignition. I have been on wild goose chases with them before. They are very critical of the slightest bit of wear in the distributor shaft bushings and the wobble inherent in the breaker plate. Is this one of the systems that the unit bolts into the stock distributor? Let me know.
Brad