Wow, playing catch-up here.
As far as the RV primaries being spheres? Go fly a kite. I personally Foucault tested several of them. Criticize the corrector if you will, but we made some **** fine mirrors.
I always assumed the RV-6 and RV-8 mirrors to be parabolic given the very fine images they produced. Very much on par with Edmund and Cave Newtonians that were well known to use parabolic mirrors.
No doubt mine was parabolized. Identical in/out diffraction pattern. It was not as smooth as my Royce.