We debated on which engine mounts to use: the early 4.2L (258ci) mounts (left) or the later 4.0L mounts (right). The 4.0L block is almost identical to the earlier 4.2s, so if you’re starting with a six-cylinder Jeep, then the mounts are a direct swap. The frame horns on a 2.5L Jeep like ours are different, but both 4.2L and 2.5L mounts simply bolt to the frame. We found a set of 4.2L engine and frame brackets (top) cheap, so we ended up going with the earlier mounts for an easy bolt-on solution rather than fabricating frame mounts for the later style. However, note that the early rubber mounts are failure-prone and the later ones have a much better reputation.