Short or long box has nothing to do with the bucket. It's the box where the trans hip bracket connects too. Top of box from frame to hip bracket about 3 1/2" short box box. 5 1/2" long box.
The bracket that is under the trans can be made from a short piece of flat steel also the bracket from the trans bracket to the frame can also be made of flat stock. These are the easiest brackets to fab up. When I go out I'll get some photos for you.