swapping in a v6 is not a reall hard swap but it is very labor intensive and a lot of things on the body need to be fabbed up to make it all work correctly. If you are interested in doing this swap PM ClayTK and ask him what's involved before you commit. The easiest EFI swaps for a 2.6 powered truck are going to be 6 bolt 2.4 and 2.0 engines they are a direct bolt on and the wiring is super simple basically plug it all in and tie it back. These engines are more reliable than the 2.6 and have huge aftermarket support, even in stock form will have plenty of power to move the montero. The 2.4 and 2.0 are the perfect NA engines to replace your 2.6 because they are inexpensive and very common so all you need to look for is the 6 bolt (early models) and in the case of 2.0 it has to be a wide block and your set.