The right combination of moderate ZDDP content (~800 ppm) and certain moly-based FMs can work in place of high ZDDP. This is the approach of HPL Bad Ass Racing oil which works well in such applications. Higher ZDDP is a cheaper route and effective.
If the '79 Vette has a stock camshaft with stock rockers and springs, the load at the lifter/lobe interface is likely low enough that a common API synthetic oil, with 700-800 ppm ZDDP, would be sufficient. Not ideal, but sufficient. In such a scenario, a Euro A3/B4 0W-40 or 5W-40 would be a better choice.
I tend to favor peace of mind with the highest quality oil available. Amsoil Z-Rod, HPL Bad Ass, Driven LS/DT, and Red Line HP is where I would look. Valvoline VR1 would be the low end option. Please, do not use BROtella or other API rated HDMOs. Contrary to internet hype, they suck.
Think of it this way. You could have a poodle or cocker spaniel for a guard dog and worry whether or not they'd be good enough, or you could have a doberman and sleep peacefully.
