Robert Shaw makes them for Stewart, they are good thermostats! 
However, many have the bypass holes drilled in them by Stewart (not all) to keep their high flow water pumps working correctly. If you have one with the bypass holes drilled into it, you may want to swap it out for one without. That little flow may be too much for your stockish engine to warm up in the winter. I don't think you should need to block the radiator airflow with a gas engine and a working thermostat.
I'm surprised learn temp is 165, many aftermarket EFI systems use 140 as a learn temp.

However, many have the bypass holes drilled in them by Stewart (not all) to keep their high flow water pumps working correctly. If you have one with the bypass holes drilled into it, you may want to swap it out for one without. That little flow may be too much for your stockish engine to warm up in the winter. I don't think you should need to block the radiator airflow with a gas engine and a working thermostat.
I'm surprised learn temp is 165, many aftermarket EFI systems use 140 as a learn temp.
