The 305 and 307 engines in the '70s had bad cams. The cams weren't parkerized properly, so they wore out really fast.
Its hard to diagnose any engine over the computer screen. I would say that the majority of cam failure is due to improper parts selection or assembly or break-in. Beyond that, I have seen tale of a few properly-done cams that went "flat" for no good reason. In those cases, the lubricants were blamed. FWIW.
