Thanks droftarts (thingiverse) for the idea to put the z-steppers on the bottom.
to do this you will need the same number of rod clamps as usual prusa (8), two more z-rod clamps, two parts made from z-motor mounts (truncated), two more bearings with washers and nuts on the lower rails, and two 18″ threaded rods in lieu of one (I think it was shorter). Note the belt goes above the bearing on the y-stepper side. The extra bushings gets the belt to miss the two threaded bars.
This is a thread reinforced automotive fuel line split with a razor blade down the center (thru both sides) for about a third of the length, split both ends. The threads keep it from twisting under torsion for light loads- like the z-axis rod coupler here. Hose clamps to secure to stepper shaft and threaded shaft. The only trick is manually center-ing the shafts- if they are not close enough, loosen clamp and try again… and repeat.