So here is an excellent example of a simple question getting completely off topic - The intent of the original query was to determine if the modern A/F ratio meters provided any benefit for use in aviation applications. There was never any intent to imply that developing an automated mixture control system was viable for most homebuilders.
WLIU makes a good point about air cooled engines not running at stoichiometric (14.7:1) ratios. But the ironic thing is that I found most of the useful discussion on the application of the A/F ratio meter on the aircooled VW racing engine forums. They agree - the 'best' ratio for engine performance AND lifespan is around 12:1 (a.k.a. - 'rich of peak'); racers have never generally been bothered about fuel economy. I was hoping to get some useful feedback on the relative merits of using only EGT for mixture control vs direct A/F monitoring or a combination of the two. It seems this simple question has hit a sensitive point for many contributing to this forum - but that off-topic discussion has served to distract from the original intent.