First, thanks again to everyone's input. I tried a Jannd Lowrider and it required far too much modification of the frame end to acquire enough clearance. I would have needed to cut away most of the end, in order to clear the quick relase nut.

The good news is: I was in Portland's downtown REI, and they had a Tubus Tara on the shelf. I grabbed it, and just laced it up. Tubus provides first-class, hardened bushings with their product, and it made the installation not only simple, but no lack of integrity or confidence. I'd received an email from Cannondale, and their suggestion was the Old Man Mountain rack line. This Tubus works quite well. All I need to find is an adapter for the Ortlieb Front Loaders so the small elliptical keeper can attach to the larger Tara rack.