Your engine number suggests a 498cc shortstroke but of course the block and pistons could have been changed to 596cc. The SV registration is an age-related one, not original. I suggest you give the info to Ian Parsons to see what there is in the Machine Register. The L/H lever would operate the half-compression valves when pulled about half way back, and then kill the magneto when pulled right back. There is plenty of info in ‘Technicalities’ if you need more details.
Brian
