what kind of gains have you all seen out of the P heads? My brother bought a crate motor that has the P heads on it, unfortunately no one makes headers to swap a P head 302 into a mustang II, so he had to pull the heads off and is going with some edelbrocks instead.
I've never seen any hard numbers of how much better the P's are than regular GT-40 stuff though.
Do a search for Thumper and go to his website, it has flow comparisons. If you have the money, go with his ported e7's they outflow all the gt40's and some aftermarkets.