Interesting R60/2

[VBMWMO]

Hi all,
I have recently been given an interesting (partly dismantled and incomplete) R60/2, and wondered if anyone has seen a similar spec bike before.
The frame is a 1964 R60/2 with no sidecar lugs, and the engine is a 1960 R60 which obviously is not original, it has the wide ratio gearbox and an 11/32 rear drive in a vented case. The dynamo is the 6V/75W and the magneto has the manual retard which I have not seen before except on the R68/69. Inside the headlamp military style green paint was visible until repainted recently. The speedo is a km one showing 23,000km. The front mudguard is missing, but the rear one is a non-standard sports type one.
According to the documents with it, the bike was registered in West Germany on 2/1/73 but the type approval date given is 6/3/64, imported to the UK 20/09/76, and has never been registered here.
It has been suggested that it could be an ex-Bundeswehr machine, and that the manual retard would have been useful when escorting slow-moving vehicles such as tank transporters, and that if it was rebuilt in a base workshop, then none of the parts would be original to one another anyway, or it could simply have been built from parts in 1972 by an individual.
Once the bike is reassembled I'll post some pics if anyones interested.
Cheers