What are a good forged piston for a standard 360 Magnum.

I suspect something like that is correct... or perhaps they are not designed to keep their dimensional stability at the higher temperatures encountered in racing use. Just trying to list alternatives, so the OP can ponder the the prices versus benefits.

(BTW, with the Magnum head's closed chambers, I am not seeing where the elevated quench pad of the KB232 is needed. Hence the KB362 suggestion....)