Can you supply some photos of the tire tread wear or is it mute point, with even wear across the entire tread?
At the dealership, I had only one verified bent rear axle housing. Every 2k, it set an anti-lock code for the rear sensor of a 3 channel system. It was a Dana 44 series w/locker. The wave washers where on the outside of the plates and thick, large and strong. They cracked, creating metal flakes that found its way to the magnetic ABS sensor. First time new, rebuilt the diff. It lasted 2k, then the wave washers broke again. Now with less than 5k on the vehicle, I had the blessing of the manufactures tech line (Who had never had one also), sent me a new housing and all new guts minus axles. The old housing had no marks on it but looking from either side, it was welded with the tube facing backwards about 3/4" of center, meaning the pumpkin was forward of center. No tire wear though, but if applied to the front, it would be tow out going forward. Could your housing be bent downward? It would be like negative chamber, but wearing the inside of the tires first. After 30+ year in the business, there is no manufactures procedure for checking for a bent housing. I would think the if axles where out, centering a laser from side to side on a paper target, should show middle at the carrier, using a suitable round bushing/bearing driver in the side bearing saddles. This should be dead center middle. Thoughts? A that time, Dana housings where made in Brazil, while the ring & pinions where forged, ground and lapped in Spencer, IA. Anything is possible.
Today alignments using software to reference the center line of the vehicle by using the rear axle first as many are adjustable. Not so much here, but would show if center is achieved.
P.S. SnapOn has a large tool box plant in Algona, IA. Small world.