When rebuilding tire curing presses, we used to shrink BIG brass bushings (12" in diameter and 6" wide") by submerging them in a tub filled with dry ice and alcohol. Once installed in the press frame, they expanded to a very tight fit. The same procedure can be used to swap the fluid bulb and capillary tube from a new aftermarket temp gauge to the head of an OEM Chevy one. Cut the cap tube a few inches from the gauge head, do the same with the replacement gauge after the bulb gets cold-soaked for several minutes, then use a close-fitting copper sleeve and solder to join the two pieces. The alcohol/dry ice bath cools the fluid in the bulb down to around -50 degrees F.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!