I never said there was a problem with using deisel grade ina gas engine, only that using it in an unknown condition engine that has been run on conventional oil could be an issue, as you do not know how much sludge or other contaminants could be in it. Plus, with the higher detergents level, it can cause seal leaks by clearing out any varnish buildup in the seals.
I know all about the zinc reduction. I also know that the oil companies test their oil on (wait for it) FLAT TAPPET ENGINES for the cam wear tests. I've been running SM grade oil in my engines, all flat tappet, one '85, one '55, and one '48, with 0 problems at all. The '85 and '48 both have stock cams, the '55 has a Howard M4F. Proper break in and assembly is the key.
BTW, Valvoline does their cam wear tests with an engine running a flat tappet cam.
