Travis,
You have a keen eye, my friend. These couplings are quite a find. We are using them on this year's robot and there seems to be no problems with them so far.
One of our students found them in the MSC catolog, and they are great, with the exception that we also needed a 3/8" dia bore.
So... we bought the 1/2" dia bore models (we had the same torque requirements), and we came up with this fix to make them work:
1. Broach the 1/2" bore of the coupling for a 1/2" hex hole
2. fabricate a 1/2" hex aluminum piece (from 1/2" hex aluminum stock) with a 3/8" dia bore and a 1/8" keyway in it.
3. Insert the aluminum "bushing" into both halves of the coupling
Once mounted in place, the aluminum bushings have no room to slide out. We are still using the set screws in the coupling, but if they would happen to back out, it wouldn't really matter. The thanks goes to super-engineer Mark Koors for making this work.
As for the torque rating, we are also above the the listed torque rating for these beauties, and we are hoping that there is a designed-in safety factor.
Andy B.