Hi AtLarge,
as far as I can see it is a Grimeca double-duplex drum brake (Made in Italy).
Was in use with MV Agusta 750 S:
http://www.motorcycle-usa.com/2011/04/article/memorable-motorcycle-mv-agusta-750s/
and some more italian bikes and race bikes in the 1970s.
Currently this drum brake is out of production, but may be appear again at even higher price.
Last price was around 1.600,- Euros for the brake only, not the complete wheel !
Cheers, Michael
