1968 Chevy C10--new carb problems

[1968]

So I swapped out engines in my 68 because of a main cap being busted and I'm having problems with the new engine. I bought a 350 engine off a buddy (numbers say it came from '77) and replaced the stock intake with a edelbrock intake and brand new edelbrock 1406 carb. It starts and idles fine but its backfiring out of the carb when goosed and seems like it lacks power. I put a new timing chain on and lined everything up correctly inside and got the dizzy hitting number one when i put it in. Problem is I dont have a timing tab on it(chrome cover didn't come with a tab), but I checked the tdc with the piston and marked where it was on the chrome cover. I set it at zero btdc with the vacuum advance unplugged. Is that right? Could being off a few degrees cause it to backfire? Should I be using full advance or timed advace? what else could be causing it? any help would be greatly appereciated. thanks