The early temp sensor hole is not a pipe thread- - - -I believe it's the same as a 5/8" coarse thread bolt- - - - - -5/8-11, maybe? The threaded bushing that's built onto a mechanical temp gauge capllary tube threads into an early head without adapters. Aftermarket direct reading gauges have one of those fittings included in the hardware kit that comes with them.
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!