The early model suzuki's (e.g. LJ50 and LJ80) had a third drive shaft between the gearbox and transfer case. They are a lot narrower than a 1200 though. If you going for a 4x4 (offroad) version, have a look around at some of the overlanders that are around. (typically a holden hz/hj series dumped on a hilux or landcruiser chassis) and do something like that.

I'd say the best thing to would be find a small 4x4 that has a chassis (one that unbolts from the body) take the body off, strip your 1200 down to a shell, and put that on top. You'll probably have to put a complete new floor in it, but that way, you have all your suspension and all mechanicals there before you start. You also don't need to worry about strengthening the datto chassis, although you may need to lengthen or shorten its new chassis.

I've thought about doing it before. The main pitfall once the project is complete, is that is more than likely going to have a higher centre of mass than the 4x4 you started with, and hence they tend to roll a lot easier than most 4x4's.