Engine model year compatibility

I started thinking about an engine swap not too long ago, and while I've postponed that with a few repairs, I still have some unanswered questions. I only recently got into Jeeps the last couple years and after my first one, I said goodbye to 'wheelin fullsizes. That being said, I am definately no expert on the 4.0, and my question is:

"What model year ranges have the same series 4.0 that will bolt right into my 1989 XJ?"

Basically my reasoning is to find a newer, lower mileage engine to buy and prep for a swap in the future. Any info or references anyone may have would be greatly appreciated. Thanks!

you're looking for a renix 4.0, they were used up till 1990.

If you are willing to swap intake/exhaust You should be able to use later model XJ blocks as well.

1987 to 1990 were compatible and completely intechangable. That being said, it's not a big deal to install an HO up til 95 or so very easily. I, as well as others, have done it and would be happy to guide you through it. No wiring, no computers or anything of that nature. Quite simple.

Cylinder head? 1987-1990 will swap with minimal to no difficulty. The intake ports were raised for 1991, so the RENIX manifold needs to be adapted to the later head (or the RENIX tbody to the later intake, or the RENIX TPS to the later tbody.)

NB: Swapping to the later style intake manifold (there were three - 1991-1995, 1996-1998, 1999-2006) will result in needing to adapt the power steering pump to the new bracket (bring the bracket with the pump,) or adapting the new pump to the lines. Also, it may require moving the serpentine belt adjuster point (since RENIX puts it under the PS pump. I believe 1991-1995XJ did as well, but I'm not sure about 1996-1998. I know nearly everything is different for the 1999-2006 intake...)

Block? Any XJ block will work - but 1991-up will have the boss for the knock sensor without being drilled & tapped. I believe it's an M10-1.5 thread. The boss should still be present - it's just the machining operation that was deleted.

Cylinder heads for the AMC I6 will swap, 1975-up, all displacements. Mechnaically speaking (they'll bolt to any 1975-up 258ci or 242ci engine block.) Most caveats above.

I am given to understand that the TJ may have had different mount pads than the XJ/MJ, but I haven't confirmed this yet. The YJ and ZJ/WJ should have used the same pads. Can anyone confirm either of these?