To swap engines you will need to install/weld in new motor mounts. Other than that it should bolt in. Honestly I wouldn't install a 258 though, there are plenty of other engine options out there. 4.0L from a newer Jeep, 4.0L stroked to 4.6L, Chevy Vortec V6, chevy 350, amc 304 and 360, etc. The...