There are two boxes that bolt in. The stock EB box and the lighter duty Delphi box that a lot of the vendors sell. Beyond a simple bolt in, there are all kinds of boxes that can be adapted - Scout, Toyota, Nissan, Big Bronco, F100, etc. All of these require different adapters, drilling of holes in the frame, and/or welding. If you are a decent welder, you can do the F100 conversion for $200 -$300 using used parts.