My swap is a 2006 Galant 3.8 with DOHC heads swapped. the Galant engine has domed pistons rather than the dished 3.5 pistons. The compression it quite high. The top end power is impressive.
I think the MIVEC would be a good choice for a truck. I have not had the heads in hand so I do not know if the standard Montero water plumbing will swap over, if it does then the swap will be easy, Most of the work will be reconfiguring the wire harness.
The bosses on the side of the block are a bit different so it will take a few hours to swap the mount brackets. There are minor changes up front for the accessory mounts as well.
Once it is running i would consider trying some different cam grinds to get the torque up. Delta cams would be good to work with for that.

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.