You could pull the tank from the ranger and put it in the montero, you'd just have to find a way to mount it. I find it easier to just use the Mitsubishi tank - it's already mounted and you have a fuel line into engine bay and a line to the tank from the charcoal canister that can be used ans the return line. Just add in an electric pump and you're good to go.

85 4x4 Pickup, 267K, 4d55 Conversion, Sway-A-Ways, Dual Batteries