The box mounts on the right frame rail, battery long axis is fore to aft.

The box I have was badly rusted on the bottom. All that remained usable was the top box frame, and the long bolt used to compress the box ends, fore to aft, and hold the battery in place. The box now differs from the original only with a replaced bottom/sides and bolts holding that part to the box frame instead of rivets.

I'll try to get pics with dimensions later today.