Keep looking for the 55-62 differentials. They are pretty available. The gear ratio will be 3.90. I believe your 3/4 ton has 4.11 gears, so there won't be much of an improvement.
IMHO, an OD transmission swap would be a much better setup. If you use a browny box, you can keep your crash box. There are several od transmissions that can be made to work using an adapter plate. Some of the transmissions include, but are not limited to the A833, Nv4500, and of course the T5.
