Zinc Additive for Flat Tappet break-in?

I spent alot of time researching and getting opinions and I finally settled on castrol 10w40 and stp.Theres some guys on another site who actually sent in samples of a few different additives and the stp was right there with all the others for zinc.They also found that the cheap stuff at wallmart was the same thing and one of the members buys it by the case.