That sounds like an incredible opportunity. I think it would be awesome to take down such a huge animal with a bow.

I am totally against high fence hunting HOWEVER I'd make an exception if the animal no longer exists in the wild. I believe there are some small free roaming buffalo herds near Yellowstone but I don't think you can hunt them (I may be wrong). Anyway, enough about that.

As far as setup, I'd suggest at least a 70 pound bow with at least a 500 grain arrow. I'd use a 1" diameter cut on contact broadhead like a 2 blade magnus stinger to make sure you get good penetration. Good luck - post pictures.