After consulting with the guy who will likely do the next motor job, I've learned that the YJ can accept a smallish diesel motor with a conversion kit costing a little over a grand. Given that the drivetrain in the KJ is very similar to mine, the clean-burning four-cylinder CRD (common rail diesel) made available as an option for Liberty a few years ago seems like the ideal choice.
Little problem, though. When I sought a new transmission to replace my disintegrating stock AX-15, the far superior NV-3550 had already been standard in the TJ for several years, making it very easy to scoop up a low-mileage wrecker for small change. (Thank you, drunk and stupid college kids! I love my new tranny!) But the CRD was never common in the Liberty, I understand, which will make it much harder to find, even given the huge number of 2005+ KJs that have surely been rolled by now.
I've tried various search vectors and online parts tools, but have had almost no luck finding a selection of these apparently uncommon motors. I understand that the same motor is used in Grumman-Olsen trucks, such as the newer USPS route trucks, and that it's most commonly used in bread trucks.
Any tips are greatly appreciated.