Oil choice for 1962 Lancer? What do you use in your Slant Six?

That slant has work hardened lifter that I guarantee are as concave as the cam is convex. I never pulled a lifter out of a slant that was even still flat, yet they all ran fine. Breaking in a flat tappet cam seems to require a dino oil with zinc, like Rotella Diesel or other that still has the good stuff in it but for a classic with 50 year old soft springs and a 98HP motor, clean oil is more important than zinc content.