I don't want to carry two spare tires. Any help would be appreciated. The 122 wagon has a different suspension from the sedan. Even if you did this, you'd still have two different wheel bolt patterns as the disk-brake 1800 rear end shares the same bolt pattern as the 140. If you did manage to change the rear axle, you could change the front hubs and spindles to the late 1800, and end up with 140-type bolt pattern on all 4 wheels.
All bearings carry industry-standard part numbers.
A dealer is not needed.