I've looked at the red9design site a few weeks ago. Now with this thread I gave it some more thought. How about removing the center block that holds the torsion-leaves, remove the needle bearings, hone the tubes slightly and make chromoly tubes to fit snugly into the beam tubes and over the machined surfaces of the torsion arms, this may be a certain interference fit, but the tubes must still be able to rotate freely in the beam tubes. Cut them to the proper lenght so that there is virtually no side to side movement. This would provide a way to really tighten the torsion arms without putting a heavy axial load on the beam tubes, except when cornering ... hmmmm .. still thinking ..
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Another thing might be to use big hardened washers over the trailing arms and over the beam tubes, machined so they fit over the welds and over the radius on the torsion arms, they do not necesarily have to be centered really, then use axial roller bearings in between, I've never seen a sealed type of these though ..
Brian