Whats the difference in GT40 and GT40P Heads?

[Coupe50h]

The p's are not really more expensive than the regular iron 40's, the p's need a special header to clear the plugs because they have a different location, also a smaller exhaust valve on the p's, but they flow a little bit better then regular 40's due to the plug relocation, of course mine been ported anyway so they flow alright..... also the springs suc on the 40's, so upgrade them if you want some real power.
the injectors? you can stay with stock 19's for a good while, i just now upgraded mine to 24's, the 19's were pushing me in the 12's with no problem, start with a fuel pressure regulator if you dont have one.