Dave:
Thanks very much for posting the photo of the tunnel site. I remember it as being easy to drive to through a foot or so of snow. We drove right up to the western tunnel face, left the 4x4 (an International Scout with a V-8), walked over the tunnel, because it looked like it would cave in at any moment, to the east end, then said to heck with it because it was so cold (no sun, total cloud cover) and walked back through it with no problem. I think I have photos around here somewhere.
That's a heck of a camera platform! A Yak 18, eh? Shades of the Cold War! Is it yours? When you're flying camera runs like this, it's probably exciting to people on the ground when they see that Red star overhead! IIRC, that was a Soviet trainer plane.
Best regards, Hart Corbett