Hi Ron, this in my eyes is a mark 1 caliper with a mark 2 motor and hub, the mark 1 hub had no rotor mount and the rotor mounted directly to the hub, there was less than 6 months between them at this early stage of development, things were changing fast.
Unfortunately most people seem to only be interested in the hydraulic hope brakes and don't see value in this early model so they are not worth as much, and as front brakes are far more common than rear the perceived value is not that high for your model. Sold with a hub you are looking at between 20 and 40 gbp, a rim would add value if it was period correct and in good condition.
To be honest the only people that seem to go for these are me and a few 1991 fisher rs1 owners.
In addition to to this yours has been modified quite crudely either as repair or to fit it to a specific fork, this will devalue it slightly so you would be looking at the lower end of my pricing estimate.
I hope this helps but your best guide of price is an eBay sale, as very few come up and you never know who is waiting.
