Help - I turned my truck into a backfiring machine!

[MattPSU]

I had my whole front end disassembled down to there being nothing but an engine on the frame. I pulled the everything off the front of the engine and I removed the intake and valve covers. I cleaned and painted the engine and then I replaced the valve covers and I cleaned up, painted and replaced the intake. Put everything back together, went to start it and it was backfiring through the exhaust. Seemed like on every cylinder. After searching the board for answers, I thought maybe I had the distributor off by 180 deg. (Of course I forgot to mark it when I pulled it out.) I turned it 180 and now it's backfiring out the carb. Wouldn't start either time...just backfires. Any ideas what I need to do to get this thing fired up? Am I off a tooth? Was I off a tooth before?

350/350 Auto w/ Q-Jet

Thanks in advance - Matt