No it’s not…
A 180 stat should have the car run at 180 if everything else is in good shape and operating properly.
How old is the radiator?
Are you sure the timing belt squeak is not a seized water pump and that’s what is causing the problem?
For Chevette parts contact: Rick Drake, Everett, WA. 1-800-247-2954. He has darn near anything/everything for a Chevette. I’ve been buying from him for a few years to keep my Chevette based British Coach Works TD running. Be sure to tell him Mark from New Jersey told you about him.
Also check out this forum: http://members.boardhost.com/Vette_Man/ It’s called the Chevette Forum.