Hiya, I am running an old flat tappet cam and lifter set-up in my 1981 Mercruiser 898 (marine 305 Chevy). After putting in the rebuild, I am using 10W40 Lucas Hot Rod and classic motor oil. It has the necessary ZDDP additive to protect the cam and lifters. Check that out if it would work for you and your engine after you replace the necessary components.