I thought this auxiliary transmission comparison was interesting. A 1969 article promoted Warn’s Auxiliary Transmission, an overdrive that sat between the transmission and transferase. By early 1970 Husky was promoting a similar sized heavy-duty overdrive that sat between the engine and transmission.
More pics of the Warn Auxiliary Transmission. This one was sold in Nevada in 2013, priced at only $450 (also included tranny & tc).
This one was priced at $700 and sold out of Maryland:
Never saw one for a jeep but good idea. Has to be strong.
Big disadvantage to change both drive shafts?
Anybody ever drive one of these? In a Jeep all three shift levers would be back pretty far. Seems like they could be stronger than the normal rear attached OD.