Mine is a C/G smoking pro , got the fire box at the same time. SFB needed no knock outs . The SP just one side knocked out where the SFB attached . You are not trying to punch out both sides of the cooking chamber are you ? ( confused ?? ) I just used a 2X inside the cooking chamber and a good hammer tap on a straight screwdriver at each of the dozen or so half moon shaped spot where the football was connected and it popped right off. Bolted on the SFB and seasoned the unit.