"Too rich, you're continuing the burn outside the cylinder into the header."

Not likely. A fat mixture will cool things down. The main problem he's facing right now is retarded timing. When the mixture is fired late, it burns late and is still burning out into the manifold/header.

wjr, make certain you know where TDC is and put 8-12 degrees in at the damper, with another 20-24 degrees centrifugal for a total of 32-36 degrees.

If you're uncertain about whether or not the damper ring has slipped, use a top dead center piston stop and find TDC for yourself so that you absolutely know.