Well, as you may already know, the XS1/XS1B axle is bolted direct to the left clampless lower, the backing plate bearing direct on that leg. The right side floats on the thicker part of the axle shaft, allowing you to adjust the right leg in/out to get smooth suspension movement, followed by clamping with its single-bolt pinch clamp.
If you look at some of the early `70s Hondas, you'll find conventional 2-stud clamp systems with drum brakes. Some used a shouldered axle nut to position the axle in the lower. You may need to fashion something like that, or a proper sized spacer that accompanies the axle nut and fits the left lower clamp. On the right side, you may need to fashion a split bushing to fit the axle to the lower clamp.
Then again, someone may have found an axle that offers a better fit...