Sounds just like worn spring bushings or just normal tolerance on axle location.
You say 1/2" more on one side than the other... so to correct it you need to only move 1/4", which isn't much at all in this case.
Check the spring bushings, axle pivot bushings, and then I wouldn't worry about it.

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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