I did it with my 65 fastback and I would not do it again. Al sorts of little expensive problems come up and almsot impossible to cool without expensive mods ($800 for radiator, spal electric fan and evans waterless coolant). The hedmans do work with about 1/4 inch clearance. To change plugs I unbolt the motor mount and jack the engine up otherwise it is a two hour ordeal. I would go with the 289 or 302, roller cam conversion, efi and aluminum heads.