Well, coming from someone who professionally specializes in under-f/4 mirrors of up to 60-inch diameters (and won't even touch anything smaller than 14-inch disks), I'd say that for your experience and tooling it's no problem for sure!
Just for clarity, I refigure mirrors of nearly any size, and occasionally make 10" and 12" mirrors from blanks that I have on hand. I just don't take orders for them. I also make smaller Cassegrain secondaries and elliptical flats.
So, yes I will touch smaller than a 14" disk.
On the subject of the Foucault, I am curious, since you deal with much larger optics than commonly encountered among amateurs, why do you think the professional community abandoned the Foucault way back in the 30's for their large observatory mirrors and bothered to devise alternative testing methods?
Simple - they didn't, and your assertion is inaccurate.
Though you are complimentary of my work in later messages, and even if it wasn't your intention, the message above implies that I use outdated methods, which I assert is not true.
The 200" Hale telescope was mostly tested with Foucault, then a little bit of caustic testing, and finally Hartman mask testing in the telescope itself. Yes, a 200" f/3.3 mirror was made mostly with Foucault testing.
While the occasional parabola might have been done with autocollimation during the era you describe (extremely large flats just don't exist, as it turns out), as I have heard and it has been described to me by those who did serious optical work during those times and at major companies, most tests were done at the center of curvature.
I should point out that for Ritchey-Chretien telescopes, autocollimation is not a null test for the primary. Testing the system in autocollimation is possible, but tricky even with one mirror complete and coated, and thus two reflections off of an uncoated mirror. One has to work match wavefront intensities and get good fringes with an interferometer. Also, the larger the system, the more vibration becomes an issue due the physical size of the test setup.
Lasers (and thus interferometry) weren't even available to most shops until the mid to late 1960s, well after the date you mention.
So, the methods that I use are time-tested and have been used with great success for very large projects. They are still used today by other respected professionals, arguably producing better end products than other methods.
However, I must say that I highly recommend use of the more modern interferometer for checking figure of revolution of large mirrors. While other tests can show when there is a problem, the interferometer will quantify and locate it so that it can be remedied most efficiently and effectively.
I would completely trust Mike ability/skill to Foucault test fast mirrors.... comes with extensive experience. The thing is, I doubt *mine* :-). Can I tell the difference in a zone null with the steep slopes of a f/4, within 1-2 thousandths?.... not so sure... :-).
Brian, give it a try. You might surprise yourself. One thing is for certain - if you never try it, you will never learn it.
While I'll try to keep reading this thread, clearly others who have been posting here have far more time to spend on posting than I do, and I don't have time to debate test methods.