I have a 1965 with 289 that's in pretty good shape; however, I would like to tear it down and rebuild, replaceing all wear items and gaskets (I don't want a race car, just a nice driver). I would like to replace the cam for a nicer sound, but I'm new to this. When looking, it asks for the intake/exhaust duration, but I don't know how to measure this and I cannot locate it in some of the manuals I have. How do I select the correct cam and should I replace the lifters and springs while its torn apart? I apperciate any help.