I don't think I have ever seen that sight before except in a picture, The bracket looks a bit like a bracket from one of the very early .485 trials rifles. The 1981 would seem to confirm this.
The sight I was thinking about in my earlier comment was the Night Observation Device or simply the NOD. Or to the crunchies, it was known as the NODDY sight! Had the same optronic internals as the old Rank-Pullin SS20/L1A1 to 7 sight