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and you need your head bolts drilled out to Half inch...


Whoa, not so fast there. Some 258's (most actually) are already 1/2". Only the early-to-mid '80s were 7/16".

The webpage that set the standard for the 4.0 head swap:
www.monsterslayer.com/jeep

The Jeep forum with the most 4.0 swap info (dedicated 4.0 forum there); www.cjoffroad.com