Welcome to the forums!
Does the fumes seem to be coming more from the front, under hood?
Did you check the fuel pressure regulator by removing the vacuum hose to it, and run car for 5 minutes, and see if the fuel starts squirting out of the nipple, indicating torn interior diaphragm?
The correct thermostat is 195 degree. Good to drill a little hole to assist in air bleeding!
I would use a Delco for replacement.