I broke my solid flat tappet in with Joe Gibbs break in oil + Lucas Zinc additive. Also only on the outer valve springs of a double set. I regularly run Lucas Hot Rod 10w-30, with the same zinc additive. Change the oil once a year.
6 years, a few thousand street miles, and well over a hundred passes and I've had zero cam issues.
LemonWedge - Street heavy / Strip ready - 11.07 @ 120