tranfer case specs

I have a 90 Jeep Cherokee (automatic) with part/full time wheel drive and need to replace the transfer case. I know I need a 242J with a 272 ratio, but am wondering if the assembly and serial number have to match up for it to work or fit properly? I want to get one on ebay, but am scared to get the wrong one. So does anyone know how picky these specs are or if any 242J 2:72 will work just fine? My assembly # is 5300 6097 and the one I'm looking at is 5300 8223 -- does this matter? PLEASE HELP!!!!!!!