I'm sitting here looking at my printer, thinking "why are there three separate parts there?"
Note: pictured model is sized for M6 threaded rods!
I've seen a few similar designs but I couldn't find them when I went to look, so I made this one myself from prusa's 'felt' Z motor mount.
Unlike prusa's felt mount, this one won't print vertically due to the bar clamp!
This eliminates the need for: 4x M3 nylock nuts, 4x M3 washers, 4x M3 screws, 4x M8 washers and 2x M8 nuts; total 20 fewer vitamins.
UPDATED 9 November
Replaced with scad that defaults to standard frame rod spacing, and an STL that has M8 holes rather than M6
Place in same folder with prusa repository configuration.scad and friends
support may assist with the 30 degree overhang underneath the frame vertex end, or skeinforge may interpret it as a bridge.