Here in Chile we have a bunch of engine conversion in samurai and sidekicks. I have seen nissan v6 3.0 l twin turbo , subaru impreza 2.0 l boxer turbo . Suzuki 2.0 I4 turbo , nissan sr18DET,Toyota 4AGE , even a toyota soarer engine 1JZ-GTE I6 twin turbo ( that one is not ready yet....they are still working on the electronics)
I haven't seen them all directly but most of them. The 4AGE toyota engine works great if want something aspirated and not turbo , it's not really big just 1.6 liter but with 20 valves , twin cam , an 4 throttle bodys ( the black valve cover one) , now if you want more aspirated power try the nissan vg30 or 6G72 from the mitsubishi montero. In the turbo side I personally would choose a nissan SR20DET but they are really hard to find as the subaru boxer and the 1JZ-GTE put worth the trouble.
I must add that this engine are not the best options for trail ridding, but in sand dunes they work awsome
samurai impreza engine
http://www.twistedandes.com/foro/showthread.php?t=56497&page=5 nissan engines
subaru twin turbo
Rugby 2.0 turbo
just my 2 cents.
cheers