I know in my slant (totally stock), I used 15-40 heavy duty diesel oil. That stuff has all the vitamins and minerals that you need. Keep in mind I did not run it very long, however every one of my old hot rod friends run this stuff with a half bottle of lucas motor honey and have run them like that for YEARS.
Also, it'll never hurt to run zinc additive in an old engine if you are scared of flattening a cam, it does not hurt to put zinc in it.
