The Sebring model car was first developed by Maserati, related or unrelated, afterwards Chrysler started making it. The Maserati Sebring convertable's last year was 1969, the Chrysler Sebring convertable is still in production today.
You could use the non-convertable seats in a convertable Sebring, but there would be a huge safety issue as you would not have seatbelts. The seatbelts are built in to the Sebring convertable seats. The bolt down assemblies for both however are identicle.
The thermostat for a 2004 Sebring Convertable is in under the water outlet for the BOTTOM radiator hose. This is behind the alternator which will have to be removed, after you remove the belts. Plan on an afternoon of work. Hope this helps.