There are a number of Start-O-Matic models using differing voltages... mostly 24vdc starting (2 batteries in series) as far as I have seen though.
The SR might also offer you an option of using a conventional DC starter as well (available in 12 and 24 volts). Take a look at your flywheel and determine if the starter ring gear is installed or not. With ring gear in place, then the starter options are a bolt-on affair.
dieselgman