Best High Zinc Oil

I don't think it breaks down any faster but they can let a daily driven engine get "dirty" inside much faster than detergent oils. Like you say that makes no difference in an engine that's "over-maintained" like these are.
I don't know enough about the cam or springs in the Chevelle... Maybe give the shop a ring and ask? I'd think the regular VR-1 would be fine for it but they'd know best as they built it.