New motor backfiring through carb

what has changed since it ran on the dyno?....did the distributor come out...did it get moved.....are the plug wires on correctly....

I pulled the distributor to prime the pump. I made to marks on the block when I pulled it and made sure the line up when I dropped it back in. Numbered on the wires when I took them off the spark plugs and put them all back on the same ones. I’m leaning toward timing right now but it was so late that I didn’t have time to really dig into it. The shop isn’t at home.