Regarding the hoops:
the 851/888 through the 955 Corsa race bikes used the hoop suspension, as well as all 93-2001 Monsters. The hoop connects to a rocker, which pivots on the frame, and is opposed by the top shock mount.
The special race models used an adjustable linkage, the adjustment was through two eccentrics (one on each side) held with pinch bolts, and 'set screws' (to align the eccentrics on each side as the eccentrics used a notched outer diameter) which controlled the location of the top shock mount pivot bolt. This particular rocker (or bridge) was made of two halves with a brace in the middle, quite different looking than the standard rocker, and the hoop bolted between the two halves rather than around the bridge (such as on the monsters).
The billet hoop shown above was one produced by either Febur or Rizoma. The Motowheels m944 had the other manufacturer's hoop:
