If you want to avoid the additives and have an oil that was designed for your flat tappet engine, plus save money on oil changes, then get Brad Penn oil. Brad Penn has the zinc in it that used to be in oil, and is priced not much higher than a qt. of the junk oil that's catalytic converter friendly.
I buy Brad Penn from the local speed shop for $75 a case. That's less than what I paid before for the newer oils and a $13 bottle of zinc additive per oil change.