Its basically a form of marketing.... "Hemi" has a nice ring to it and everyone knows it now whereas the majority of consumers don't know anything else other than V6 or V8. Sort of like the Hondas marketing of "vtec".
While its real engine technology, its not the end all solution. ... its just a technology that has a marketable name.
I don't think theirs any way possible a 5.9 would fit due to both the weight and heigth of the engine. It's a HUGE, HEAVY engine! LOL. You "might" be able to fit a 4BT cummins in there though and they are pretty bada$$ engines. And as far as the "hemi" thing goes pretty much any modern OHC engine has a "hemi" chamber in them. It was high tech stuff back in the 60's but nowdays it's just a gimmick because when people hear hemi they think a firebreathing 426 hemi making waaaaaay over it's 400 something hp it was rated at.
2007 JK unlimited rubicon, red rock crystal pearlcoat, rc 2.5" spacer lift, 35x12.50 goodyear mtr/k mounted on black 15x8" mb72's. (Mine)
2005 WK Limited 4.7, QTII, Midnight blue pearlcoat. (Hers)