Hi Terry, as Brian says the '48 parts book shows an apparently unhinged guard, part no. 67-6752 but it is listed as " rear mudguard with fixed fittings". Also listed is part no. 67-6753 - "rear mudguard tail with hinge".
The straight stay, 67-6758, is shown with a forked end which would indicate a hinged guard. Stay length, if you need it, is 12 3/16", hole centre to hole centre.
Looking at pictures in books, it is difficult to tell. The official factory pictures appear to be touched-up photos and a lot of detail is missing.
Trev.