They should work fine. The only difference I am aware of is that the GT40 P heads take a slightly different header than stock or GT40 heads. The intakes should work fine.
Not sure if they have the air passages drilled that connect at the rear, but you may not need them anyway.
I have FRPP GT40 irons on my 79 Capri 5.0, with a Holley 4 v intake, etc, and BBK shorties.