Looking for a source for a new thermostat for this engine and whether the factory Thermocon specs called for a 140 or 160 degrees for an open water cooled sytem
I'm guessing by open water you actually mean raw water or sea water cooled system. That is, there is no coolant tank or heat exchanger with your engine. If so, as of January 1971 CC said the Q series motors will have a 143 degree to 165 degree bypass type thermostat.
For the closed cooling system (does have a coolant tank and heat exchanger) the thermost is a 140 degree to 165 degree bypass type thermostat.