Here is a Lucas Oil Zinc Chart.
https://lucasoil.com/pdf/Zinc_Values_MotorcycleOil.pdf
What's interesting to me is their Hotrod and Classic Car Oil which I have seen at my local Speed/Performance Shop @ $5 qt +/- has a Zinc content of 2,100 ppm. Lucas Oils and additives are in use all over the mechanical world with great success, I'm also quite sure their engineers did not simply throw a dart at a chart to decide on the ZDDP ppm ratio.
I purchase any name brand oil of the correct viscosity, usually on sale, and always add 4 oz. of Lucas ZDDP for my satisfaction.
Witch Craft? Maybe ...but I run 2 flat tappet motors with zero issues.