There are... assuming you're referring to the 3.7L V6 used in the Liberty/Cherokee. The 3.8L was in the early JK Wranglers, IIRC.
TwoBobsKJ wrote a good synopsis of an engine swap in a KJ and some of the critical differences across the years. You can swap a different year if you are willing to do some additional surgery on the donor engine.
http://www.jeepkj.com/forum/f202/engine-swap-overview-53270/
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2008 Liberty Sport 4x4 Automatic
Jeepin By Al 4" Lift Kit
BFG KO2’s 245/75R16
Full MOPAR skid plates
Rock Lizard Skink Super Sliders
AtTheHelm Front Recovery System & Roof RackM116A3 Trailer build thread: viewtopic.php?f=72&t=77997