Your steering issues can probably be solved with new kingpins, tierod and draglink ends, and adjusting and or rebuilding the steering gear box.

For a rear axle and brake swap with lots of gear choices I'd use a GM 14 bolt from a cab and chassis truck.
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=599879#Post599879

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-