What kind of legwork did you mean for gaining access to private land?
I intended to steer you toward officers of the Nebraska Game and Parks Commission in the areas under consideration for your hunting trip. Specifically, I was thinking that they may be able to recommend some favorably disposed private land owners you might contact to ask for permission to hunt on their property. It looks like you have already done something like that.
I grew up hunting upland game and waterfowl on ranch land in the Sandhills. Our family was fortunate to have access to some very good hunting during that time. However, the kind of access we had was solely because my grandfather grew up in the area and knew the land owners very well.
Without knowing someone in the area, I believe that your best chance at hunting private property would involve getting out and about in your area of choice and getting to know some of the local land owners. It seems to me that there is just no substitute for "pressing the flesh."
Anyway, that was the thinking behind my post. It looks like you may already be well on your way to finding what you are after. Good luck on your hunt! Please let us know how it turns out for you.