these look rather neat & cheap. measures amps/voltage/rpms.
http://cgi.ebay.com.au/Tacho-oil-and-volts-gauge-set-genuine-Equus-NEW_W0QQitemZ350076249964QQihZ022QQcategoryZ102561QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
would of been better to have water temp instead of rpms though, thats what the tacho is for... looks like it might fit into a din slot too so i'll probably enquire about it.
or even this one
http://cgi.ebay.com.au/Temp-oil-and-amp-gauge-set-genuine-Equus-NEW-BARGAIN_W0QQitemZ270251360409QQihZ017QQcategoryZ102561QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
temp/oil/amp individual gauges.
might have to ask for better photoes & do some measurements.