After I made that post I went out and took a close look at my rockers. They're not concave. That must have been an optical illusion. Once I got them under a strong light and put a straight edge on the surface, I could see that they're actually convex with a radius. There is a slight depression in them where they contacted the valve stems but I'm glad to report they're not actually concave. They looked that way in the dim light of my garage, just taking a quick glance.
Anyway, they look very fixable.
