it is very possible to bolt the 4v heads onto a 2v block, however you will be down on power because of a loss of compression due to the 4v heads larger combustion chamber. if you plan on going with boost this is a good thing, however your stock gt bottom end will be spitting out rods if you crank the boost up too high. if i were you i would recommend using a 96-98 cobra block (Teksid) build that with low compression/high boost in mind, forged rods, forged pistons, and a stock forged cobra crank. going with ARP main and head studs is another good idea. i recommend the Teksid because that is the strongest OEM 4.6 aluminum block that ford used. btw it wasnt made by ford it was made by the Italian company Teksid. if you dont mind using an iron block, then pretty much any romeo or windsor block should safely support 600hp with the aforementioned internals.