You can use a 12-volt meter
Is a six-volt tach/dwell meter available anywhere? Or is there a 12-volt meter that is switchable to six volts? The Actron Co. makes a 12-volt tach/dwell/volt analyzer (#CP7605) that can be used only on dwell mode.
Could a 12-volt tach/dwell be used on a six-volt system if it is connected to a 12volt battery? What about if it is connected to a 12-volt battery charger? I would appreciate any help/direction that you can provide.
I could not locate a tach/dwell meter specifically meant to be used with a six volt system, but there is an easy solution to your problem.
A 12-volt tach/dwell meter will accurately measure the engine rpm and dwell angle with your six-volt vehicle as long as the meter is powered by 12 volts, so all you have to do is connect the meter to a separate 12-volt battery or 12-volt battery charger set to trickle charge.