We have been there the last two years for antelope and we had a great time. Most of the public land where we were is surrounded by private ground. There is plenty of block management land to hunt though, and it also doesn't hurt to ask some of the locals if they will let you hunt on non-block management land. Also, it's been our (limited) experience that when they agree to let you hunt, it doesn't hurt to give them some razor clams, smoked sockeye, halibut, or something else that doesn't grow in Montana. They seemed to appreciate it almost as much as I appreciated the use of their property.
Like Craig said, do your research, as the past few winters have been brutal on the antelope populations, especially the further East you go.