One that contains the necessary additives for a flat tappet cam. Since the advent of roller lifters in production motors, those additives are no longer present in the oil and you will wipe out your cam lobes in short order. STP or other additives are available for purchase. Some oils are marked for use in older engines, but I don't know which ones. If your car has been driven a lot in the last 30 years, it may already have lobe damage. My 80 Pontiac wagon had such damage when I bought it.
NO! 10w30 gives faster oiling on startup, as well as during winter. The 10w stands for the viscosity at 32 degrees. The 30 stands for the viscosity at operating temp. It's the best of both worlds.
