Take the current arches off, I'm not sure how they are held on a ZJ but there's likely to be some brackets that need drilling / cutting to remove. The YJ arches are made to fit a flat body panel and the ZJ is all curved like and XJ, maybe worse. I would suggest putting loads of masking tape on the wing and then using some clamps like welding clamps, woodworking clamps etc to test fit them a few time until you are happy, then mark the masking tape as a guide for cutting. You might need to cut the mounting surface of the YJ flares to get them to fit too.
When putting TJ arches on my XJ I went for as much clearance as possible while trying to make sure it followed the vehicle lines at least slightly.
To fit I used rubber bungs with threaded inserts, can't remember their proper name. It required drilling 13mm holes and then using M6 set screws and washers to fix, but give some 'give' to the fixing if that's something you want. You might need to strip out the inner arch liners to help with this if you have them still.
