Can you tell me what size carb goes in a 2001 325 trail boss? Is it interchangeable with any other carb?

I've searched and searched for what it has. Mikuni, yes. Tried searching with numbers on the side. No info.

I've gotten schematics but can't find the size. Ours is messed up, jet housing and air/fuel screw housing both stripped. It's pretty beat to say the least. Btw, what's up with where that mixture screw is? Can't get to it at all without taking it off!

Got the quad in a trade and don't want to put a bunch of $$$ into it. Any advice/info would be appreciated!