8 3/4 Thrust Block

Quote: I realize the thrust block shifts to press against both axles but suppose the combined axle length was too great [or the axle tubes were a bit too short] preventing the bearings from seating fully. I just can't see proper seating of the thrust block and axles at the same time. Maybe the machining is just more precise than I imagined?

That's why the axle bearing retainer on the passenger side is threaded. Install the axles both sides then screw the retainer in until both axle end bearing are seated in their cups (axle pushes against the thrust block which pushes against the other axle which seats it's bearing in the cup). Once the screwed in bearing retainer is snug and you've pulled back and forth on both axles and they don't move then back the retainer off until you've got .010" passenger side axle end play. Reinstall retainer lock.