You can run a 22" wheel on a WK with a 265/35-22 tire. 20"wheels aren't a problem either just stay under 9" wide with a 275/45-20 tire. A good example is the SRT8 comes with a 20" by 9" on the front but can accommodate a 10" wide out back.
As for the Overland it isn't really a big upgrade over a Limited. The suede inserts, wheels and other small touches but electronics and mechanics are typically the same. You can find those amps a dime a dozen in wrecking yards across the US. Just make sure it has (had) the same head unit yours had. Being an Overland I'm guessing you had the Boston Acoustics system and REC navigation/changer head unit. So check for Limiteds or Overlands and you should find a compatible amp. The SRT8 did have an available Kicker sound system upgrade which uses a different amp so I personally would limit my search to just Limited or Overlands. This is the info to the best of my knowledge and can be worth what you paid for it. I just know how it can suck when nobody replies when you ask for help. But I just recently did an upgrade on my WK sound system so all this info is still fresh in my head. Here is a picture of the amp from WKJEEPS.com. Good luck with your search.