In talking with Matt McCormick, I think I'm going to try his method of leg attachment by bolting straight to the frame. I'm not doing the 2-3-2, so bolting the legs straight to the frame shouldn't be a problem. When Matt did this, he shored up his side uprights with another piece of 3/4" ply on each side. So, I've done the same.
After Matt's R2 made his debut appearance at the Sci-Fi Horror Convention here in Sacramento last year, there was a bit of sway in Matt's frame. After adding the additional support, that sway went away, so this should work out pretty well. I've seen Matt's droid multiple times and have noticed nothing unusual performance wise. Stay TOONED!!!!!