Hey plains hunter, I really don't know whether the Dumbell ranch is open to antelope hunting or not but unit 69 is nearly all public anyway. I saw a ton of pronghorns in there last fall late in the season on BLM land. What I didn't see was anything over about 12" of course I wasn't actually hunting 69 just looking it of for a possible future trip. I would concentrate on the eastern 2/3rds. of the unit for quantity of animals.
Good luck in the draw!