2018 136 HR Ont.
A long time ago I had a roommate/workmate who used to work in an automotive spring shop, everyday. He was intimately familiar with spring work. I've r&r'd a few rear axles and the procedure was always the same, locate the spring perch on the center bolt, period.I became intimately familiar with the simple arrangement when I removed the helper springs from my van.
Search for rear axle leaf spring wheel alignment and see what you find. I'm sure people have paid for 4 wheel alignments but didn't actually get 4 wheel alignments when they have a solid rear axle on leaf springs.
On our vans if one side was 1/8" forward and one side was 1/8" back the axle would be out of alignment by about 1/4 of a degree. Formula 1 might care about that but your local expert alignment guy will laugh at you it you mention a measurement that small. The book guys can check my math but I think it's right.