I looked at some unused oil analyses of older oils at Blackstone, and it appears that gas rated oils got reduced zinc and phosphorus as well. I saw some as high as around 1500 ppm zinc and 1500 ppm phosphorus, and later oils are below 1000 ppm for each.

Kevin
1951 Chevy 3100 work truck
Follow this saga in Project Journal
Photos
1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.