Nice project ,Geoff.
I can recommend using a Ronchi grating on a star as final check /tweak on correction. Foucault reduction can often be misleading if you are inexperienced. I say that because I tested 30 or more amateur mirrors when I used to work at AstroOptical years ago and only found one ( an 8" F7 ) that produced a decent star image on the bench
I'm sure that if these guys had used a simple grating on the a real star to check their figure , they would have ended up much better mirrors. I even remember one which the owner assured me had a 1/10 wave figure- it might have but it was in the wrong direction - an oblate spheroid instead of a paraboloid, which would have been instantly diagnosed using a grating
