Engine still not right after timing set

If it was hung open, you would get a random pop out the tail pipe from un burnt fuel igniting in the exh tract.

Like a misfire? Cause I was getting that kind of noise, just figured it was from the timing being off.

Was it running well before the distributor hold down bolt came loose?

Yes.

As for removing the headers, it wasn't to change the plugs but to attach the machine to check pressure he said.