I got another set of parts today. These have a couple improvements.
The idlers are fixed. There is no more binding regardless of how tight you make them.
The o'ring spacing has been adjusted to the actual cross section (0.139") of the rings. This allows them to be placed side by side without bumping into each other.
The rings have been move virtually to the edge of the wheel. Now a work piece would have to have about a 60 degree angle leading to the wheel before it would miss the ring.
Tim Wehr, also gave me a suggestion on the rear adjustment. This uses two plates instead of one. The front plate has angled slots and the rear has a horizontal slots. By tweaking the relationship between the plates you get a smooth range of adjustment. The dual slots, keep the spacing equal (in a perfect world). I am an optimist, so I am going to give it a try. Hopefully the way it slides in the extrusions keeps everything squared up.
The whole assembly can be flipped if the direction of the angle works better the other way.