I've been thinking for a while on this and I've found that the 3/4 technic pins fit perfectly into the center hole on the PF motors and spin freely. If an alternate 12v-style wheel was made which accepted a technic pin rather than an axle, then it could be used in combination with 3/4 pins for the two center wheels, and the axles could be reserved for the driven wheels. The center wheels, with the added benefit of less friction due to riding on pins instead of axles, might serve well to minimize the drag created by using axles w/ stops, as well as removing the need to trim lego (always a plus).
The 7760 is nearly complete now (still have to attend to the wheels and invest in the larger windows)-
and I've started work on a 7755.
While my current electrification setup is all 9v I plan on using the 12v center rail system for these two, in addition to my (currently PF) 3677. Part bb0053 looks like an easy way to add 12v pickups for these motors, and doing so is cheaper than buying 12v (or even 9v) motors.