Go to RockAuto.com and choose 1961 C40 with 261. They show all sorts of options for a 2-1/8" Thermostat. The ones we get for our 235's are about 1-5/8" or so?? (maybe not) Not sure if those are the same ones as NAPA.
After researching every year at Rockauto, I am more confused than anything. I don't think any of those are the ones you are looking for. So, anecdotally, it is going to be very hard in the future to find thermostats and gaskets for that housing. The 235 ones work just as good and are very plentiful. Just something to think about.
