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.

1999 Montero SAS'd on Kings and stuff

1998 Montero trying to get a V8 Swapped