My understanding is that the zinc additive provides a higher lubrication level than the oils without it, which is needed because of the flat tappet design of the older engines.
Correct?
This is correct. I'm using JG XP4. After I had the motor dynoed at Top Of The Hill Performance the owner Craig Hill said to use this oil to keep the cam and tappets from wearing out. I've got about 15,000 on the rebuild with no issues.
