You must really be bored!
A B6000 is a gray market tractor with some age on it, so it's a project finding parts. You can't go to Kubota Corp. and get a parts list. The PTO shaft rotates the opposite of most tractors so hooking up common PTO powered equipment isn't an option without a "reverser". They're difficult to find, and when you do it's $800 or more.
I think to put a 4x4 front end under the tractor isn't a problem, but you will probably need a different transmission to hook up power. I'm not positive....but I'd find one and look at it,.
Hopefully, someone more knowledgeable will give you the definitive answer.