72 360 first start question

good advice, thats what i started doing actually. I was just worried that it could ignite through the line back to the tank somehow. firing order is definitely correct, would too lean or too rich cause a backfire. this carb had been running great on a 318 about a month ago so I don't think the lien mix could be that far off?? i have the vaccum port on the distrubutor roughly facing the #4/#6 spark plug as a starting place but I can't seem to get it to idle worth a crap either by advancing or retarding. after priming i installed the oil drive gear facing #1 and then the distrubutor as well. I'm sure i was at TDC. so I'm a little stumped. could it be valve lash? I just had the heads rebuilt. I know you can't ever assume the machine shop did a good job but i wouldn't think i'd have a dead valve.