Savarin -
Will you have any kind of added friction? I can't imagine that you'd want such a high magnification optical instrument to be too loose. Several years ago I built a Dobsonian scope (in a class taught by John Dobson himself!), and used polyethylene drawer glides riding on a piece of acrylic for the azimuth and on ø6" anodized aluminum rings for elevation. Stays put nicely, but quite easy to reposition.
PS - I've been watching your build posts with great interest. Absolutely beautiful work!