Gah, this looks more involved than I thought! Worst comes to worst, I have a few good LBSs around. The rear hub looks to be... 150mm??? That can't be right but it's the same width on my IGH 8 speed. And the frame is steel.

Is this something that I should be looking at a custom built wheel for then? My IGH 3 speed bike has a width of 130mm, but it doesn't look that much smaller then the one I want to convert.

Edit, derailer as tensioner. The derailer on this bike is really big, and since this is a foul weather bike, kind of half the problem. Ideally, it would be something small. I'd like to get that 'magic' fit but I don't have a pile of cogs laying around to try, LOL.