There are tacho's available for the single cylinder engines - however most of even the aftermarket will only run 4-6-8 engines... which means they wont work with the singles and occasional twins used here...
If you want an analogue tacho it would be worth looking for one from a motorbike proper using a single cylinder (which could be anything from a 125 to a 750).
The other problem is going to be electrics although you could probably run the thing off the white wire if you are using a chengine...
Jemma xx