[mopar man]

I have a 79 chevy big ten with the 350 of course and it ran good only mis fired with the quadrajet when i really romped on it so I awitched to a edlebrock 600cfm carb and with the stock intake had to say bye bye to the egr and plugged all the old vac lines and when she first starts up backfires on the driver side and when i give it gas it will back fire i suspect timing is the issue but can it also be a lean backfire how can i test this? and i also switched to tubular headers and its open for now till i can figure out this issue it also dies when I put it under load ex put it in gear any help would be hugely appreciated