My wife and I hunted C about 12 years ago. I believe since then, the dow separated a small portion of C, to form Y, that topgun is talking about. Topgun please correct me if I am wrong. We hunted around Gillette and didn't do any good, then we went over south of Buffalo and killed two small four point bucks - if my memory is accurate, I believe we were just west of Kacey.
Area C is tough, as I would speculate it is 95 percent private - but I could be wrong, I am just going off of memory of research.
There are a couple of parcels of state property, one is just to the southeast of Gillette. Sorry, I can't remember exact roads, but I do remember it was several miles southeast of Gillette. I remember there being several square miles of walk in area, or state lands of some kind. Anyway, it was nice country, and I was told that there were some nice bucks there, both mule deer and whitetail. But again, that was about 12 years ago, and a lot has changed in that time.
As far as antelope, I cut my teeth on unit 23 antelope, and had a lot of great times there. But again, with the mostly private area, you need to get a landowner list and start calling landowners. You should have no problem finding a place to hunt, but you need to call as early as you can to reserve a spot for the opener. If you aren't going to be there on the opener, you can almost choose any landowner you want and be able to reserve a couple days to hunt. Good luck, my wife and I had a good time while we were there.