I can't recall his name, but we did have a member of the forum who bought one of these bikes a couple years ago. or, perhaps he took a street model R65 and modified it to GS setup using R65 GS parts and pictures.
The army/military is more concerned with tractability and the ability to operate on various qualities of fuel more than top speed, so it is no surprise that these were fitted with the lower insurance class configured R65 engine at the time.
That could be a fun rig - it has the late 80s monolever swingarm too. Once could drop in an R80 engine pretty easily for more excitement - provided one didn't try to squeeze between too many trees!