Hi Bug. I bought a project bike (a basket of bits) a few years back, it came with a trick rear end, developed for track use, then replicated for a few Guzzi enthusiasts.
I have some background details but cannot get to them for a few weeks (I'm travelling away from home).
It's now built up, but a work in progress - still to fit proper wheels/tyres, the cans are too noisy, the shocks are way too stiff, etc.
I'll need to strip the back end down sometime since I have a leaking oil seal - you are welcome to come and check it out when I do (this summer, perhaps?!) Located 20 miles south of Oxford.