AOutfitter, Looks like you're good to go. I shot my buffalo with my .54 Hawken. One 435 grain Maxi-Hunter just behind his shoulder did the job.
Rob, Ft Peck is 300+ miles from where the buffalo come out of Yellowstone Park. They may have migrated that far 200 years ago, but now they just go a few miles.
Flags, You lucky dog. I've been putting in for that hunt since they started giving out tags for it.
As to the LOL comment about the OP's hunt, I don't know the details of this hunt, but my experience with both private and wild buffalo, both inside and outside the Park, is that they are not that hard to get close to. Probably not much harder than sitting in a tree stand overlooking a food plot and shooting a whitetail buck in it with a centerfire rifle. I have hunted bighorn sheep in Montana's unlimited tag units, and have been close enough to hear rams eating grass and to have hit a ram with a small rock thrown under handed. I practice enough and am confident enough with my centerfire hunting rifles that I consider anything within 300 yards a "chip shot." The hunting part is getting close enough to make your chip shot.