It's not practical for my needs (too small), but I think along the same lines. I'd love to take one of those transits and make it 4wd. I'll likely never do it, I still have to finish my Syncro 4wd conversion and I just bought a 07 E250 which will be my new full time rig. ( I really want to Cummings/4wd swap it but if that happens it wont be anytime soon)
Now keep in mind, this is me not even looking under the hood of a connect, but I think if you are to do this you might as well go "all" the way real 4wd not some AWD hack set up. IMO the best way to go about this is to gut the van remove the uni-body tub and rebuild the tub so it can sit on either a jeep chassis or a 4wd ford ranger chassis. If you go to that trouble, then might as well swap in a VW TDI turbo diesel.. If I were to build one of these that's the way I'd do it.