Bill, I asked Orion Optics to regrind an 8.5″ mirror (I’d had the home made Newtonian on its end for a while and the diagonal fell onto the main mirror – an expensive mistake – I won’t be doing that again!) and then re-silver. The accuracy claims were very good, although I’ve no means to prove it subsequently.
However, I found the people there very offhand, arrogant even. That was c. 6 years ago so they might have changed out.
Your mirror looks (and weighs) amazing! By the way when my mirror came back it was only half the original thickness!
Good luck. Paul