You have the odball block that as far as I know was only used on the pre 87 auto tranny Monteros and RWD's with the torque-flite auto tranny.

A possible solution is to get an auto tranny from a later Montero ( 87 and up) to go with the more availible blocks. That would get you a 4 speed auto and if you get a later V6 unit you can get a lockup converter as well.

In general all V6 units had a better torque converter.

Do you know what the gear ratio in your axles is? I think the gear ratio was a bit taller on the 3 speed auto Monteros. That could be a deal breaker since you would need to swap a lot of parts to get the 4 speed auto to work right. At that point just fixing the original type wide 4 makes more sense.

Kevin C