Is the punch mark really at either 6 or 12? The cam must rotate into it's correct position as you are installing it. I suspect it's one or more teeth off the correct position, maybe. 6 or 12 won't make any difference as long as the piston is at TDC when you install the cam, but when you set the valves, you must set them with the piston at TDC after the intake valve closes, not on the overlap between the exhaust stroke and intake stroke. That puts the punch mark at 12 o'clock, and that's why we set them up that way. Do I make myself clear?