I’m with Gord, I bet if you take it to an Auto parts store you will find a match.
Opening temp should be written on the Thermostat, do NOT go with a modern auto 195f thermostat as I bet the one for your engine is more likely something a lot lower temp.
By being fresh and raw water cooled, we refer to them as fresh water cooled
I have only seen a thermostat on the fresh water side, the raw water side flows freely and dumps in to the exhaust
, so you don’t want a thermostat or anything to block flow there.