I can't see any other way to achieve the alignment you have other than the center having spun on the tubes.
What about the joint formed by the axle tubes/perch mount radius?
Consider what would happen and those welds had failed. You know how sometimes a welded joint will crack but, the fracture is not visible to the naked eye - without dye checking or the application of an external stress (like prying on it with a crowbar).
If those welds failed, the only thing keeping the axle tubes in position relative to the springs/frame would be the clamping force of the u-bolts (and whatever resistance to rotation the shocks might provide). So, assuming the inner ends of the tubes were still securely welded to the differential housing - if a sudden, heavy load were applied (like described below):
I don't know if i mentioned it but i was peeling out and got some bad axle hop. Ever since then about 40 in 3rd gear and 35 in fourth have reallll bad vibrations and i can hear it i wanna say howling.
the resulting torque might be enough to cause the entire rear end assembly to rotate.
That's just something to consider.
Again i'm just not convinced its spun none of the plug welds are broke, the tubes look like they've been at the same angle for the last 30 years of their life.
It hasn't been noted yet, what type of axle we are discussing - at least I didn't see it. But, if it is a 14 bolt (it's probably a 10 bolt and I am not too familiar with those), you should be able to use the bolts that secure the brake assemblies to the square mounting plates at the outer ends of the axle as a reference.
I
believe that the mounting plates are targeted for welding in such a position that, if an imaginary line was drawn through their centers and extended forward - it would run parallel to the axis of the pinion shaft.
I probably am not explaining myself well, here are a couple of visual aids to help:
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And remember, the relationship shown above would remain like that, even with the installation of a lift kit using tapered blocks - or if the perch welds had failed. Because in either of those cases, the entire rear axle assembly would rotate as a single unit.
The only thing that would disturb the angle of the brake mounting bolts to the pinion center line would be if the axle tubes had spun inside the differential housing. In that case the square plates/bolts would be still held stationary by the perch/u-bolt assembly - and so would the axle tubes. But the differential/pinion shaft would be free to rotate in relation to the tubes.