IMO, budget is the limiting factour here. As we do not get the plethora of Isuzu and Fuso trucks and buses found in Australia, there aren't many parts from which to chose. Yes, you could get a manual transmission in a 2WD truck, but good luck finding someone who knows the various bolt patterns, tail shaft dimension and degree of interchangeability between makes, models, years and packages.
Contrast this with an NV4500, for example, where a company like High Impact, can make that transmission fit nearly any application. Companies like Quick Time will make custom bell housings and companies like TWF and Advance Adapters can mate their transfer cases to dang near anything.
Could this same goal be accomplished using all Mitsubishi parts from various years and models of trucks? Probably, but I would not have a clue where to tell you to start looking for that detailed information. No dealer in the US is going to be able to talk to you about bell housing bolt patterns or tail shaft conversions on a 2WD six speed manual transmission.
I will be interested to see what you come up with. Good luck.