82 TA, I believe you are on to something.
My truck does indeed run very cool. Years ago, I was having thermostat sticking issues and as you mentioned, many people go to a lower temp thermostat. That was my reasoning also. I also reasoned that small, 4 cylinder aluminum head engines (being more susceptible to overheating and head warpage) could benefit from a lower temp thermostat. Lastly, I thought that as long as you got the cat hot before the smog test, you were going to get good numbers.
All that being said, I just might try what you said and switch to the factory thermostat just before my smog test.
Thanks for all the replies!