The SOM has a number of differences, much heavier flywheels, often referred to as electric flywheels, start/stop solenoid assembly that controls decompression and fuel pump rack. The SOM system is quite complex, consisting of a generator/starter, alternator control box and Start-O-Matic control box. Adding the SOM system to a 6/1 SOM engine at a later date, even if you could find the parts, would be quite difficult. Also, SOM's were supplied on a specific base plate that mounted the engine and generator. You could use a 6 or 8/1 SOM engine to drive another generator and make your own base plate, control system etc, but it would not be a self starting and stopping set like the SOM, unless you also added a starter motor and control system.