Been thinking more about this Fargo, and the whole adventure bike/monster cross thing. I had some time after coming home from the IMBCS time trial, and went to work in the garage.
The 2.1" WTB NanoRaptors are SO close to fitting that it's not even funny. Plenty of (well, enough) clearance in the front, and a slight bit of rubbing on the chainstays due to the side knobs. Even if I file them off, it's gonna be pretty tight. I'm going to try and track down some 1.8" tires this week and mount them up and see how it goes. If I can get them to fit, I'll break the setup on the double gravel century this weekend.