What I did was to use the wire struts that came with the robart retracts. I mounted them into the retracts and cut them to the length suggested in the Robostrut installation instructions (about 1/2" exposed stub).
Next, I cut the robostrut to lenght (about 4 7/16" from the center of the hub, or 4 5/8" total length).
The robostruts come with an adapter bushing which will fit inside the end of the Robostrut and will slip over the wire stud mounted in the retract. Mix up some JB Weld and apply it to the outside of the bushing, then insert the bushing into the Robostrut until it fits flush with the end of the strut, and let cure.
Drill two holes through the strut and bushing, and thread them for the set screws provided. Insert the strut over the wire stub with the strut hinge pointed foreward, attach the wheels (I used Robart 3 1/2" wheels), mount the retracts, and start making adjustments for your alignment. On my installation, the wheel just cleared the main spar and the rib just outside the wheel well. Once I made all my adjustments, I removed one set screw and drilled a small indent into the wire stub, replaced the setscrew and repeated on the second set screw. This is to prevent the strut from rotating during takeoffs, landings and ground operations.

Hope this helps,

Scott