I know this is an old post but here is the answer to your question. Bud Rosenburger, from
www.budbuilt.com, made the adapter. The bellhousing was taken off of the rear tranny and an adapter was made to mate the two together. For highway driving, you simply put your rear transmission in 5th gear. Every gear below that is just another level of reduction. This setup gives you 50 forward gears and 4 reverses. If you put both trannies in reverse, this is your lowest forward gear. You cannot run a setup like this unless you have a long wheelbase vehicle. I dont have any good pics of the trannies but I do have a good side veiw shot of the truck. The 79 long wheelbase truck, now sports a 91 4-runner body, due to extensive body damage on the truck. The dual trannies were built as a prototype for testing porposes. The adapter is not manufactured. You should see more of this in the future because UNBREAKABLE is getting ready to build a new truck with dual trannies and 4.7 gears in the t-case. That will be a slow mo fo.
All this pic shows is a good idea of drive shaft length needed for this setup.
Keep in mind that this is a long wheelbase.
Thanks
Shawn C Groce
