Easy people. most everything is the same from the 2.5 to the 4.2. I did this swap about 6 years ago.Outside of new bellhousing, input shaft on the trans, clutch slave and line, mounts and frame buckets and exhaust, it went together fine. Wiring will all work on the 2.5 or 4.2.
jduress - shoot me a pm and I will give you as much info as I can. One word of advice, collect as much as you can of the new 258, like all the accessory brackets.
It's just a Jeep, and if you don't wheel it once in a while, it's not even that.