The bushing that the Temperature Sending unit is threaded into is pressed into the left engine head. Removal of that bushing is tough with a slide hammer but much easier with a puller. I believe all of the Thunderbird parts suppliers sell pullers but if you are after one in a hurry here is a simple one I came across from an East Coast Thunderbird friend.
Get a close pipe nipple of the appropriate size (3/8 or 1/4 based upon year) insert a bolt through the nipple. The bolt must be large enough that the head of the bolt won’t go through the nipple but as small as possible. If necessary grind the points off of the bolt head so that will slip inside the threaded bushing on the engine.
The bolt must be long enough to extend through a 1” socket. Assembly order is:
Bolt inserted through pipe nipple Bolt passed through a 1” socket Washer placed over the bolt on the socket Nut placed on the bolt Thread the pipe nipple into the threaded bushing until firm Tighten the nut on the bolt The bolt head will grab the pipe nipple and pull it and the bushing up into the socket
When replacing the bushing use a little sealant to ensure no coolant leak