Update.
Been messing around with this thing and we're almost there. I saw it sort of working last Sunday, but not as good as it could be, then I got told by another guy that he'd sussed it and saw it working last Tuesday.
In the mean time I have become an electronics wizard (NOT!), and have read just about everything there is to read on the net, downloaded a million and one data sheets, and built a couple of prototypes.
I actually had the RC valve operating nicely(ish) on the bench relative to rpm. I called Paul in to see all proud of myself and then **POP**. Oh well...back to the drawing board. Hopefully my friend's is more reliable than my first attempts.
Built myself a shifter light while I was at it though. this electronics game is incredible. I rejected electronics at college and went for mechanical engineering. I wish now that I'd done both.