Unloaded, I'm thinking you are right.
Someone might correct me on this but ...
Look at your first picture. In my mind the square axle
coming out of the axle
tube and into the torsion arm should be offset 45 degrees from the square tube of the axle at rest (unloaded is not at rest). If you think about how these are made there are 4 pieces of rubber that fit into the "corners" of the axle tube around the square axle that joins the torsion arm. I believe they alter the angle in the original casting of the torsion arm in your axle.
From the picture, it looks like you could run a straight line through 2 corners of your square axle right to the center of your spindle. My guestimate would be that you originally had a zero degree axle.