like i said...
xj's have p215's stock, right?
same as YJ's
they are about a 27" tire
the swampers are 29's exactly
they should go no problems minus some fender contact at full flex
possibly some rubbing on the control arms at full wheel lock as well
i rubbed on the front leafs pretty bad up front when i turned sharp corners (U-turns etc)
this can be fixed quite simply...
as jo mentioned get some coil spacers up front and either extended shackles or lift blocks for the rear.
or get some after market rims
they will likely rub on the LCA's at full steering lock though. used to run 235/75/15 which is like 29x9 I think(correct me if im wrong) and they rubbed my LCA's at full lock a bit. now I run 31x10.5's and they really rub at full lock(like dont go to full lock unless I really like ripping the lugs off corner of tread)