I also like Bradpenn oil, if you ever get around it, put some on your fingers and pull it apart. It' stringing and very hard to get off. It will still be hanging on the crank when you are ready to start it, no matter how long it sets.
As far as the Zinc amounts, your engine has very little valve spring pressure even when wide open, so any oil you choose will be good enough.
That's what STP oil treatment does, it's very stringy, and according to their info, contains ZDDP. I have actually used that at full strength in my Model A tranny. Wasn't very good when temps got down near freezing though. I nearly bent the shifter one morning trying to get it into gear.
