The 351W E7's are the same cc's as the 5.0 heads. 64+ or - 1-2 ccs. Only difference between the two are the bolt holes. If you want flow AND compression port the C5 heads. Only way to equal that with E7's is to mill the crap out of them. The plus side of E7's are the induction hardened seats, but that only goes so deep into the iron. Work them too much and you're back into the same iron the 289 heads have. Another plus to the E7's are they readliy accept the 1.7 "Cobra" roller rockers which can be had used for $100. With a mild cam, they're a good bang for the buck, you get .030 more lift, plus the reduced friction from the roller trunions. Ford says they're good for about 15 hp.