I have an early "S" Type Jag (1964) actually and I an considering up grading to engine to a 4.2lt But would like to keep the early style head. Just for looks with every thing polished they look rather attractive for an old car. I had in mind a 3.8lt head to match the 4.2lt. I have worked on all the earlier engine and later ones doing all sorts of performance mods but never a mix and match. I may fuel inject it to help with economy. Any helpful advise is appreciated.
I cannot help you directly buddy as I am not familiar with these cars, hopefully somebody will be along who has a greater understanding of these engines.
When you get an understanding of your next move, how about starting a project thread as this sounds very interesting. Once you have reached 10 posts then you will be able to post up photos of the project as it progresses.
