I put the meter in a Jaycar plastic box, and mounted the sensor in a bit of 1" tube which clamps into the tailpipe. Copied off the one GR uses on his dyno.
I've now wired the 12V with both alligator clips and a cig lighter plug, so I can even run it on my Jeep.
I didn't dash mount the unit, IMO once the mixture has been sorted out it's about as useful there as a vacuum gauge...

Only down side to the tailpipe sniffer is it's useless at idle. But I hear if you shove some copper tube in it to reach up into the muffler, it'll work OK.

Pics-

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Thankz doc for the explanation. cheers

Put 170 mains in the weber today and the flat spot is now gone.

Originally I thought my flat spot was just a dizzy advance problem so I bought a dial back timing light.
In the end I had to -
Replace the blown GT40 coil with a GT40R style and put a ballast resistor in for the elec ignition. The Crane Cams people recommended the Fireball XR700 run a ballast resistor setup. Apparently these modules don't like 12v.
Changed the dizzy curve by removing a spring.
Tweeked up the weber to suit my engine.

Goes great now, Thanks everyone for the input.