Late model rear end

You can use the shorter axle in the other side. You are not supposed to switch sides on axles after they have already had stress in one direction. But given the lack of power in an exploder I wouldn't worry about that. Of course a new short side axle would be best. We used to do this exact thing in the 70's. The early 70's Econoline 1/2 ton vans had a 9" with an offset. The short side axle was about 25" long. We would shorten the long end on the housing and use two short end axles making a rear about 52" wide. The only drawback was the large 5 x 5-1/2" bolt circle, if you call that a drawback.