I have a 90 2.5L w/ manual trans. The radiator is shot. I plan to swap in a 4.0L or SBC (still waffling) down the road a bit. I would like to use the radiator for a 91+ 4.0L now, to avoid swapping it later. Can the 4.0L radiator be made to work with the 2.5L?

 

The two use a different shape radiator. The following links have the dimensions.
1990 2.5l https://www.summitracing.com/parts/SGT-CU871/
1991 4.0l https://www.summitracing.com/parts/sgt-cu1193

 

In your first link if that application lists a Comanche it must be ****ed up, it's got to be for a wrangler.

This one on Amazon says it fits both/both:

 

I don't trust Amazon for proper fitment. In the review someone says that it is not the correct one. Will fit the MJ and XJ with the 2.5L or the V6. But not the 4.0l. Simple mistake for Amazon to make.
https://www.rockauto.com/en/catalog/...,radiator,2172

 

https://www.sunbeltradiators.com/sbr1193

 

I fitted the 4.0L radiator to the MJ today. Fairly simple. Remove the 2.5L radiator, condenser, and all associated 2.5L radiator specific brackets. The 4.0L radiator bolts right in, no mods needed. I used the 4.0L hoses and just had to extend them. I cut the top hose right beside the a/c compressor and added in a 9" long section of pipe. Cut the bottom hose beside the air box and add in a 6" long section of pipe. The MJ already had the stock mechanical fan removed and a large electric fan in it's place. I will mount that fan to the 4.0L mechanical fan shroud. The remote power steering reservoir was mounted to the side of the 2.5L radiator mounting brackets, will have to mount that with some redneck engineering. Last issue is the condenser, the 2.5L setup had it mounted aft of the core support. To retain the a/c I will have to get a condenser for a 4.0L.

All in all, not a mod worth doing if you are retaining the 2.5L. Considering my plans to swap out the 2.5L, it is worth the effort for me. I don't plan on swapping out the 2.5L for a while, I have a couple other projects ahead of this one. I would like to have the truck functional if the 2.5L will run.