after lots of messing around i have devised a super cheap CO meter,ok not 100% accurate but near enough,what you expect for £4 ?.
ordered one similar to this 85C1-V Class 2.5 Voltmeter DC 0-5 Volt Wht Panel Meter

mine is 0-1 volt,connect it to earth and output of lambda sensor and watch the vlotage.
0.45 is 14.7-1 or near enough,up to 1 v is rich,lower is lean so you can twiddle your megasquirt etc and have an idea where you are going .

A moving coil meter will almost certainly present too much load to an oxygen sensor, they have very high output impedance. Using a digital multimeter would work ok, but narrow band sensors are pretty hopeless for setting anything other than a stoichiometric mixture.

i had thought about using a digital meter but watching a needle seemed a lot easier than constantly changing numbers.
anyhow,as i said it works as a guide

Narrow band sensors tend to switch about the stoichiometric point and really only show rich or weak. They do not give a linear output relative to air / fuel ratio. This is why if you look at a lambda waveform from a normal tin top the voltage oscillates between around 200mv and 800mv with the ecu trying to average the readings.

I did build a device years ago with a LED bargraph but gave up as it didn't really gives meaningful readings.