'75-'76 heads have 60-62CC chambers, larger intake ports, and smaller 302 valves. '77-up 351W heads have 69CC chambers, small intake ports, and small 302 size valves. '75 is a change over year where Ford used up their remaining larger 351W valves of 1.84/1.54 until they were used up and then put the 302 valves in so about 25-30% of '75 D5OE heads have the 1.84/1.54 valves and the rest have 1.78/1.46". In '76, they all have 302 valves. One more tid bit of info for those who think '69 and '70 351W heads were special with smaller chambers of 1-2CCs. They had a slightly different height valve seat which made the valve sit higher and thus reduced chamber volume a little. If you are putting 1.94/1.60 valves in '69-'76 heads, they will be the same and only not grinding the seats down much will actually reduce the volume to 58CCs with the valves sitting high which is better for flow anyway. I have CCd many sets of '69-'76 heads but nobody here believes what I say because their "book" and other people who live by the "books" say different. The true 351W 4V head with casting number C9OE-G is the most common true 351W 4V head and those valves sit a little higher(stick out in the chamber more) than some '70 and all '71-up heads. Essentially the '69-'76 351W heads are the same castings with different revisions for smog and little revisions for other areas except the intake ports and chambers. Only unnoticable little variances to the exhaust ports. Now let me hear the "No that's wrong because my book says something different or my friend said the opposite". Reality bites!
That's understandable. It was just quote that I read off of another tech board from another site. So do you think that a set of pre 75 351w heads mildly ported would be a good cheap upgrade for my 85 GT?
Yes. If you don't spend the money for new valves, screw in studs and guide plates, new guides, & resurfaced. If it's a guide knurl, valve job, and resurface it would be a cheap upgrade. Valve job for stock and larger than stock valves should cost the same and make the valves stick out in the chamber farther while e-bay has 1.94/1.60 stainless valves for $48 a set(I have bought 2 sets for my 351W heads already) and that would be a cheap upgrade. About $55 after shipping and are very nice valves for the price. $100 to remove studs and machine for screw in studs. $25 on e-bay for new screw in studs and guide plates. That would be a good and fairly cheap way with good parts. Your '85 302 would run much better from the bigger valves, bigger intake ports, and higher compression. Those heads can be milled .030-.040" without any intake alignment problems and increase compression even more.