I fitted one of these last week: http://www.digital-speedos.co.uk/rpm...eter-320-p.asp
Unit is made by Koso in Taiwan. Their website is very useful & they emailed me technical specification in 12 hours in very good English!!!!
Fit the gauge to homemade bracket to handlebar. Run wire down to spark plug. Wrap wire around HT lead & secure with cable tie. Couldn't be easier......