I seem to be missing something here------I'm trying to give an example of how to get a square to the world axle mounting at the wheelbase you want----
And it seems that you want the fender well to look right????????? That comes down to the idea that you should have your tire/wheel combo fiqured out, on hand for mockup into the fender to determine where you want the wheel to be--------and then mount the springs so the axle center line swing will be there.

Of course this assumes that you have the placement of the body on the frame fiqured out--on an original frame/body that is pretty much a given, altho on a repro body, fabricated frame you do need to (and lotsa guys don't) mount things where they compliMATE instead of compliCATE matters----

As far as moving the spring center bolt hole in the axle bracket, do so equally as it will effect the spring rate at the axle-----