Tony, I don't know if youwouldbe interested but if you have both heads , ( Mercury and Ford ) note that the Ford head hasa "Shallowerer" combustion chamber in it . I was told by amachinist years ago that by using a set of Ford heads on a Mercury engine , you could bump your compression by about five points . Since I wa already having to swallow the high price of fuel in 1983, I decided to not do it . I still have the heads and mabye I may still do it too. Ed Shaver