I did a swap from the parts Eagle, an 82. Any 258 81+ Some 80s AMCs were holdover blocks and didn't have the mountings.
The 4.0 block is cast but not always tapped for the brackets. There are of course a number of small details, just brows for some swaps on here.
If you're in a hurry, drop one right in, It's a weekend project with a hand or a couple of weekends on your own. I kept my original intake and exhaust due to the emissions setup, make sure you take pictures and notes as you disassemble.
You may want to have your head rebuilt because the chances of finding a non-plastic valve cover is slim. Of course you start down that path and it can turn into a 4.0 head and new cam.
It's probably best to start with a budget and price what you want, then add 10% for surprises.
Summary:
80+ Eagle
81+ Concord, Spirit; 258
81+ Jeeps; all 258
87+ 4.0; with minor work
Other engines require crossmember changes or welding to work.