The SOHC 24 valve 3.0 engine (along with the SOHC 12 valve 3.0 and the DOHC 24 valve 3.5) was available from Mitsubishi in some of the Gen II Monteros, although it's somewhat rare. The engine should be able to be transplanted without too much difficulty (plus you'd be able to use all factory parts), although the wiring harness would need some modifications.

95 Montero SR
3.8 MIVEC, Advance headers, 2 1/2" exhaust, Magnaflow muffler, OME shocks & rear springs, 2" body lift, 3" tank lift, 4.90s, TRE front locker, factory rear locker, Roger Brown Rock Sliderz, 315/75r16 (35") tires, Sport big brakes