Did your Stevick-Paul get completed? I just completed a 160mm f15 version. (I had a very long focus primary, but anyway had to refigure it as it had shocking astigmatism which I only discovered on assembly of the telescope. I made my own convex secondary and concave tertiary. All coatings apart from the quaternary flat are silver, for best reflectivity.
I did some investigation with the OSLO-edu optics software and it appears that tolerances for focal length and spacing along the optical path are actually quite loose. It's just the angles which are a bit more critical. Collimation has gone quite well and i get nice views but at 160mm aperture it's no light bucket. Mine has a tube for the secondary/tertiary/quaternary mirrors and focuser, while the primary is slung below the tube via a hexapod truss allowing both angle and position adjustments. I have a thread over on the ATM section of the big other astronomy forum starting with C.