Might I suggest going with a V8 discovery transfer case instead of swapping out the diffs? 1.2 instead of 1.4 high range. Probably a little bit of an easier job and can drop your revs down some. Also retain the nice 5.57 diff ratio if you need it off road.
Jame's hopefully this picture will make sense, Theres a 2x2 alloy angle channel that run's around the side and back riveted to the body. There is then a closed foam strip that the roof sits on, the roof side cladding then conceals the strip for added weather proofing. The hing is not visible at all, its a 3mm thick stainless steel piano hinge thats the full width of the body. It bolts to a 2x1 box that bolts to the windscreen frame, the 2x1 sits on its end with a 1x1 box welded along the front edge flush to the top. The hing sits on this, directly behind it is another 1x1 welded to the 2x1. So in effect the hinge sits in a steel L shape, the front of the roof that bolts to that is a 2x1 box on its flat. Its fit's very tightly together and so far ive not had any water come in at all along the front, with the roof up or down.