They are not press fit ! They screw in with special sockets. The hex shape should be a clue. Well its not hex but a special shape like oil senders and such.
Just had mine replaced in my 68 on Thursday. Friend of mine has owned a garage business for 30 years, and he had the special sockets to screw them out and in with. Mine were a real bugger to get out. I swear they were the originals. Air wrench wouldnt take them out. Had to use a 5 foot breaker bar.
The 68 are threaded for sure. Dont know when they changed from that.