I've bought two pipes from Carpy, the first one a CB550 pipe three years ago. I couldn't get it to fit to the head at all. He did take it back and refunded my money. I tried a CB750 pipe from him last year and it fits perfect, sounds good, and I made a homemade bracket to secure the tailpipe.
Oh, and the MAC pipes sound like a choked engine through a tin can (IMHO). I have one on my 550 and hacked off the megaphone and installed a reverse cone.