[paul2748]

Every body has a different opinion about this. I heard from a noted Yblock engine builder that any oil with a 30 weight or greater has enough zinc in it for Y blocks and I would assume flatheads. So I 10/30, 10/40, 20/50 should be sufficient without an additive. 60's oil had less ZDDP (zinc blend) that most of the oils noted above. He uses Valvoline 10/30 or 10/40 conventional in all his builds


But as I said, every one has a different opinion on this.