Resurrecting an older discussion here... but I am wondering if anyone has tried using adjustable lowering blocks as a way of dialing in alignment of the rear axle housing? The version in the link below appears to offer a large amount of adjustment, far more then ever needed. Although I'm not a big fan of the lowering blocks due to causing other alignment and leverage issues, this concept looks interesting for tweaking the alignment. If offered in a 3/4" steel version I might try them.
Speedway Adjustable Pin Racing Leaf Spring Lowering Blocks