[NotchJohnson]

I cant help you out with the part numbers, but if you look at the heads (you may already know this), the gt40 heads will have "gt" cast into them, and the p heads will have "gtp" on them. I am almost positive the gt-40p heads flow better than the standard gt40's, and I know the combustion chamber is smaller, I think by about 2cc??? Im sure you know that if you happen to find p heads you will need different headers. I have ported gt40s on my car, along with a ported cobra intake, 65mm tb, 75mm maf and 1.6 rr. The car pulls really hard past 3k and keeps pulling all the way to 6k. It definitely has more power up high. You will be impressed with the power, but I would definitely change the intake as well. I hope this helps you a little but, Im not sure what you already knew, John