Actually, believe it or not google turned up a review of what (I think) is an addon for a flight sim. Within this, was a fair amount about the Litton thingy. I'll see if I can find it again.
Edit: Here is the review. There are about 500 words about the Litton LTN-72 INS and a nice screencap of it showing the display, rotary switches, and buttons, and some interesting info about the 'eight waypoints' rule.
http://www.avsim.com/pages/0700/toff...re747200.shtml
I followed some of the links and there is a download for a manual (15mb!!) and in all probability there will be a big section on the nav kit, as according to the piece they spent most of their time on that.
Edit2: Now I know the model name, (there is also an LTN-92, apparently. Presumably that looks less like a 1970's Soviet calculator) I've been able to search more, but bizarrely enough, it's all flight-sim stuff. There's bound to be an operators handbook somewhere online...