I think your truck came with Aisin Waner AW-71 automatic transmission and they have a interchangeable bell housing. The bell housing found on the AW-72 found in the 1st gen Montero with a 6G72 swaps onto the AW-71. I've got this setup sitting in the back on truck because I was thinking of a V6 swap. You will just need the flex plate from a 6G72 because the torque converters are the same.

Anyway, Salvage Auto Supply in Charlotte has a clearance sale on a SOHC 6G72 for $65 with 142K and DOHC 6G72 for $275 with 159K. So consider a V6 swap.