Hello...I want to install OEM 6V temperature sensors in my '57 292 heads and get the dash temp guage to work. The car came with a freeze plug in the passenger side hole where the temp sensor is supposed to go. The driver side has a threaded insert installed for an aftermarket sensor that is too small to accept the OEM sensor.

I've not done this before. Can I buy threaded inserts that press into the freeze plug holes...or do I need to thread the existing hole in the passenger side and drill-out & thread the hole on the driver's side? Thank you for your response in advance...Bob