Any newer diesel will need the ECU that came with it. The easiest way to do it might be to swap in a Mitsu JDM engine.
Only the 4m41 is ECU controlled. But there are 2 types of the 4m41; the first one, that came in the 3rd gen is direct injection with electronic pump and the second/newer(2006 and up) has a common rail system. I'm not sure if the CR engine is available in the US, but if it is it's deffenatly the way forward.
4M40 and older diesels practically swap themselves, 4M41 wouldn't be too bad of a swap though.
Would you be better getting the engine from another LHD country than getting one set up for rhd and trying to adapt bets to fit?