Good to know. Apart form the plug angle is there much dif between the GT40 and the GT40P? Did the GT40 come in alloy?

The GT40s on the EB GT, Sprint and EL are iron.
Yeah can get them in alloy, I think they are a different casting to the original iron GT40s though, there are probably a few different castings floating around.

I don't know the exact differences between the 40s and 40Ps, you'll get ALOT of info on this subject if you google or check some US mustang forums though.

gt40Y is an alloy casting nearly identical to the gt40p. Slightly larger vavles IIRC. There is a GT40X which flows alot better than both of the above too. It also is alloy.