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And second question, are you using any sort of an adapter plate to get from the output to the 231? I know the 231 is round, but the output on my trans looks square-ish..
The transmission in your rig was also used in many Jeeps as well as other rigs. You want to get the tail housing from late 90s Jeep that had a 4.0. There is a writeup where Nathan C installed a dual 231 into his Montero, this will give you the proper model. Nathens Dual Xfers

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.