Needing a Square wave RPM pulse for RPM signal for AEM AFR

[J666ERA]

Hi

Not a MS MJ question but as I have fitted these before and there was a wealth of knowledge and help I thought I would try here.

I have fitted a AEM AFR Failsafe gauge to a classic mini in a race series, we have to use a carb and dizzy so cant go MS sadly.

Fitting the gauge is great but it needs a square wave pulse, and the Lucas Dizzy and coil gives a messy RPM signal.

AEM are little help they suggest the MSD tach adaptor might be the thing, but have never used one and cant even tell me if the gauge needs 5v or 12v square wave.

So I came here and came across the coilx and tachx, could one channel of the tachx clean it up and convert or the coilx? I have also had it suggested that all I need is a pair of diodes reversed in parallel and a resistor after them to chop the top and bottom spikes off the signal and trim the voltage, but no suggestion of values.

Any help out there?

thanks in advance.