I have searched on the issue and it seems that I cannot find a definitive answer, just a bunch of posts saying it should work. There is a 95 sohc 24v 3.0 in the local u pull it and the 6g72 in my 89 knocks so loud, I can feel it in my teeth when I start it up. I could grab EVERYTHING with a 30 day warranty for $250. The only hurdle I see is wiring harness and the 95 is an automatic, while my 89 is a manual.

As I understand, both engines share a bellhousing bolt pattern as well as numerous mounts/bosses for the engine mounts on the side of the block, and Mitsubishi built the pilot bearing into the flywheel, which will bolt up to the 24v 6g72, right?

It bolts up but it's not plug and play, manual or automatic isn't the issue. The 24v motors have a way different injection system, you can do the swap but you will need to swap wiring harnesses. Look up PA_JERO's 3.5 swap, you'll be doing the same thing minus the motor mount relocating and bellhousing/TC swap because his was a 4 cylinder.

V6 for V6 is a bolt up but not the wiring.

I cannot speak for Monteros specifically but I have in fact swapped a 12v 6g72 for a 24v 6g72 on two separate occasions in the past. These were both on Dodge Stealths. Taking from that experience, you will need the main wiring harness and the ECM. For those swaps, there were other things that also had to be reworked. The wiring to the alternator was not on the main harness and completely different. This had to be repinned. The MFI relay was different. The cruise control did not swap over correctly. You may encounter other body wiring harness that do not swap over correctly like the dash and speedo/tach harnesses.

Your best bet is to buy the entire truck so you will have everything you need to complete the swap. Then give the body back to the junkyard to crush (if they agree to such a thing).

It is at a u pull it yard. they wont sell whole cars, so that rules that out, unfortunately. If the biggest concern is wiring, I think I will be o.k.. Worst case scenario, I have to megasquirt it. As long as everything bolts up, I am happy.

With the Automatic, I had a 4cyl auto, I had to swap the bellhousing, and use a 12v 3.0 starter and flex plate. Also have to modify the back engine plate. I'm pretty sure at one point I remember reading somewhere that a 24v 3.5 bolting into a gen 1 required frame engine mounts to be relocated as well like mine required. You also need a BFH for the fire wall. With your swap, your starter will work and your bellhousing. Your fly wheel and clutch plate set up may be questionable but I honestly think it will work.

If you can, please post a progress report. It's a long time wish of mine to upgrade to the 3.0 24V.
Thanks!

What is the difference in HP between the two?

Javy