What's the best way to fix aluminum intake threaded hole for temp gauge sending unit?

Can u reach the bottom of hole from stat housing hole? If so I would be tempted to use JB Weld, whatever type works for aluminum.
Wrap the sensor in Teflon tape real snug, slather the JB Weld on the sensor and in the hole. Thread sensor in the hole gently/carefully, let fully cure, remove sensor and tape from hole. If you think it will drip and can reach thru stat hole, put something to catch/clean up.
Good luck.