Unless you have a 305 already there, you would be better off going with a 350. Its the same size block but more power, cheaper, and easier to find. I just did this about 6 months ago, except I yanked out a 304 for the 350. You will need new motor mounts, either bolt in or weld in. A transmission adapter depending upon what tranny you have. Possibly a new radiator. I used a 350 swap kits that included a new radiator and motor mounts from 4x4 parts i believe. Since I also swapped in the Chevy tranny and T-Case I didn't need an adapter. Everything else is pretty straightforward, as long as the new motor comes with all the brackets and such.
2013 Commando Sport. Rock Krawler 2.5" X-Factor lift. 35" MT/R's, 17x9 Pacer black wheels. ProRock 44 front axle. RCV shafts, ARB front and rear lockers. 4.56 gears. Coast 1310 drive shafts. TeraFlex adjustable tire carrier. AEV front bumper. Warn 9.5 CTI winch. TrekArmor seat covers, Spiderweb shade
Build Thread : http://www.jeepforum.com/forum/f96/c.../#post15031329