I've used the <A target="_blank" HREF=http://www.bobcat.com/cgi-bin/view.ssl.ind.cgi?model=463>Bobcat 463</A> a few times, and it's one powerful little machine. It can squeeze through a 36" door and do a lot or work. No belly mower, of course, but with the Bob-Tach system, you can probably stick one on the front.
From memory (take with a grain of salt) the B7400 minimum is ~ 38" and the B7500 is~43". This is with the tires all the way in. Also there is a narrow version of the B7500. I don't think Kubota makes a loader that is less than 42" for these tractors.
Al
87 Ingersoll 444, 84 Ingersoll224/'44 GreavlyL/60'sGreavlyL/49 Ford 8N
The Ingersoll would be something to look at. Not sure on the exect size, but they are small, and built like a tank. A new model they just came out with also has 4wd.
John Deere made a version of the 4100, the 4100N that is specified at 36" wide with the Ag tires, but they don't list a loader as being available for this model. Maybe an after-market loader could be fitted?