I did that crossing in 1979!! (Sorry for the interruption!)Just happened to be the one I remembered passing when doing the Lakes crossing from Bariloche (Argentine) to Puerto Montt (Chile) in 1993. Was quite overcast on that second day though, so didn't get a good view of it.
I have done the Bariloche to Pucon crossing a couple of times, it is just north of this one and goes past the Lanin volcano. The guide on our trip gave us an interesting story of a previous trip. The tour company was Australian and at that time they were using Victorian sourced and registered bikes and support vehicle.
Bingo. All yours. I just love Chatwin's description. I really fell in love with that part of the world. Any town with Snail in its name is going to be memorable, one way or the other. We turned west and camped in "nowhere" then picked our way along a seldom used dirt road on eastern side of the border up to Los Antiguos.Baja Caracolles ?