Couldn't find anything about JKR but I did come across chaps these down south:
Some good technical detail on both turbo and supercharging. The more I read the more sense a turbo makes over a supercharger for these bikes. Cheaper, to install, lower maintenance costs, runs cooler with better economy and less weight, and boost is not determined by revs but throttle opening, which would better suit these relatively low-revving engines. I can see the sense of putting a small supercharger on a screaming inline four, many of which hit the limiter at twice the rpm of the Rocket. From the factory the Rocket has quite a soft throttle ramp. Coming off a closed throttle is smooth and easy. A turbo would retain that and at low speeds and light throttle openings it would feel much the same as the naturally aspirated engine and be perfectly manageable. The boost would come when you start to wind on but without having to wait for the revs to build, which would suit the natural power delivery perfectly.
My ideal set-up would be 250 bhp and 190/200 ft/lb of torque, if that pairing is compatible. It would also do away with the dilemma of which exhaust system to use. (incidentally, I thought that bike at Elvington looked far better with it's compact turbo unit than any aftermarket exhaust option I've see to date).
I think those sort of figure could be achieved with relatively modest boost and would be more than enough for a road bike. I would anticipate some internal engine upgrades but nothing extreme.