The centrifugal clutch showed up. I had to turn off the original sprocket, and need to weld a new one on. I don't think it'll be this one, I might mount this on a shaft running through the old bottom bracket, then I can gear up the engine to get it spinning fast enough to engage, then step it down again at the rear wheel.
I chopped up some old bars, then dug out some inverted levers that I bought in an auto jumble ages back. Again, they had to be modified (turned down in the lathe to fit), but look just the ticket!
One will definitely be the rear brake (disc), the other either a front disc or possibly the throttle....
Got a set of white tyres coming - £8 the pair!