You can bolt on a Dana 300 t case to the Mitsu auto trans and then run Toy axles, I'd run the 80 series axles though because the old pickup axles are weak and if you don't truss them they will bend. I'd also look into longfields if you go with pickup axles.

1999 Montero SAS'd on Kings and stuff

1998 Montero trying to get a V8 Swapped