Can you recommend a good rev. limiter?

[itdontgo]

I've just changed 6 valves in my Kent engine after I buzzed it last time out. It has a nasty 3rd gear that car and it's really easy to miss it going up the gears and get back on the gas before it's fully in.
I designed this:

www.shiftlight.co.uk

The way a shift light or rev limiter works is by measuring the time between pulses coming from the points or ignition amplifier in electronic ignition systems. If it was a nice clean 12v - 0v - 12v - 0v it'd be easy but it's not so simple. In the software we have a timer to ignore what in electronics is called ringing coming from the coil. That's where the voltage swings about for a while until all the energy given to the coil dissipates. If you didn't have this you would see a load of pulses for a few miliseconds and think that was the ignition. We've had to make this variable as on some cars the ringing can go on for ages. Additionally, we have set up some hysteresis so that you only see a light if on the last stroke of the engine there should also have been a light to stop it flickering when it's close to the correct engine speed.
I can understand why some limiters just don't work as they have to be universal and have to see through a lot of electrical noise and variability in timing to decide when to cut the cylinders. I also can see how they'd never have saved my valves.
Anyway I'll probably make my own for my car which firstly only works when I've just come 100% on, off and on the throttle (just when changing up) and also operates only when the engine speed has increased after just coming off the throttle (why else would that happen if not a missed gear?). Also none of this soft cut ******** the ignition is off for half a second or a second or something. A bit of fuel in the exhaust isn't as bad as a piston hitting a valve.