First thing, for even mildly technical questions you need to completely describe the vehicle in question. What year, engine, transmission, transfer case, options, modifications, etc.
Over the years XJ Cherokees had different engines, transmissions, and computer ignition systems, so the correct answer to most question will vary based on the model year, and the optional equipment, and/or modifications installed.
Next you need to explain why you wanting to use non-standard exhaust and cat converter parts. Do you have links to, or part numbers for, the stuff you are looking at ?