Will 1975 vintage 115 HP heads fit on a 1981 vintage 115 HP Johnson 4 cyl cross flow? Will they bolt up and work? I realize the compression would be higher but would it be too high? The coils would have to mount some other place but thats not a big deal. Is it do-able? I want to raise my compression some and I can get a good deal on the early heads but I don't know if they are 100% compatible.