No. The plugs, reguardless of size are going to hit the primaries. The problem is that the plugs are in a different angle than typical Ford heads, and come almost straight out of the side of the head, and straight into the header pipes. The "P" headers come straighter/further off the heads to clear the plugs. MAC shorties will not clear, but MAC full lengths will because they come out far enough to clear them.
Anyone saying they're using short plugs or certain headers, are either extremely lucky or are running regular GT40s, and not the P's.