What could cause this? 360 problems ####update####

Rat Bastid said
It may not be your F’up. The tolerance stack up may be enough that dot to dot was retarded enough to hit the exhaust.

Degreeing the cam would have avoided that if that is the case.

Timing set could have been mismarked. This is a prime example of why you should degree every stinkin cam. performance or not.