Not to be harsh but if you're worried if the factory shifter can be adapted to work then a swap might not be a good idea. Making the Montero shifter shift (insert trans here) is going to be one of the easier parts of the swap.

Being a Montero guy to the core i like to keep as much Mitsu in my truck as possible, but i am also on a thin budget so i build trucks on the cheap. My suggestion is use the drivetrain that already matches the motor, this will make your life easier. If you have the funds or the MacGyver ability i say go for the LS1/Aisin combo, other wise make a check list of things you'll need for the complete swap. Plan on clearancing things under the hood, frame modifications, component relocation, custom mounts and crossmembers, DO A BODY LIFT, think about oil pan to differential clearances and don't forget custom driveshafts.