I did that with my 77 landcruiser...was a bit much for the tranny and was always overheating...
Aye, I did put in an NV4500 Truck tranny, never did have an overheat problem, though on hot days I do have issues with the gasoline getting hot and vaporizing in the front tank and the lines (the front tank has an external pump, while the rear tank has an internal pump)...I have pondered putting a heat exchanger on the fuel return line, though not really sure where a good place would be