After finally giving in and installing an in-bed filler cap, I finally took my old K10 for its first ride in more than 20 years. Made it down to the local parts store to pick up some heater hose.
There is still much to do, but it made it there and back, and the engine doesn't smoke or make any weird noises. My only glitch during the test drive was my own fault; I forgot to cotter pin the clevis pins for the rod that connects the transfer case lever in the cab to the lever on the transfer case. That lead me to a question.
I think the truck is in 4 wheel drive, possibly 4 wheel low. The front hubs are unlocked, but I cannot turn the front drive shaft with the transmission in neutral. The gearing also seemed to be rather low; I wasn't comfortable driving over an indicated 40 MPH (I haven't checked for speedometer error yet).
Once connected, what is the quadrant for the transfer case shifter? The pattern is long gone from the knob, there is no sticker in the cab and the owners manual (yes I have one of those) isn't clear. Before the clevis pin fell out, I had the lever all the way forward, which seems correct to me.