There are multiple oils on the market that already have the higher zinc quantities and are specifically formulated for our flat tappet cammed engines. I like amsoil products, however there's joe gibbs, brad penn, valvoline, etc.

I seem to recall reading that indiscriminately adding zinc products to your oil can be detrimental if you overdo it. That too much zinc can cause pitting and some other chemicals that come along with these additives can cause issues if overused. Calcium levels in the additives or something if memory serves.

I would also add, that if you have stock cam/valve springs, any oil oil will be fine.