CA;
I must agree with Derek...once adjusted, there is little need for constant monitoring of the A/F Ratio...it doesn't change as a rule, and if it did due to something inadvertently changing at the carbs, throttle response (or noises, or other indicators) would likely give us an indication and clue to check it out...
I have located a Tach (actually an 1800 Smiths type) similar in location to that shown by Mike, at the right side of the instrument cluster:
...but on my LHD, this puts it more toward the center of the car, and line of sight, which I prefer...but again, a Tach is a "dress-up instrument", and not really a crucial instrument, unless you are going to be shifting at high revs repeatedly, and need to know RPMs accurately...after a short while, you will be shifting by the sounds from the engine compartment anyway...
Cheers from Connecticut!