Bob,
My info. comes from not only the major
oil makers but from Duke Williams who has written many articles in collector car mags. and happens to be an engineer who developed many HP motors for the "big 3". Do a search on him and you'll find the truth about motor oils and it won't be from someone who is trying to sell you something. His advice is followed by car collectors (myself included) that have cars worth 100's of thousands of dollars.
Jim
PS It's
Zinc and phosphorus (not mag.) and even CJ-4 has 1200 PPM just like the old days.