Any suggestions for removing the steel square hole pipe thread plug from a 95 LT1 aluminum head?

Have the engine up and running in a 37 Chevy and need to leave the OEM temp sender on the drivers side... would like to install an aftermarket temp sender in the plug hole on the passenger side head for the dash temp gauge.

Torqued a little with a square head socket via a 3/8" drive ratchet...but just get that "feeling" that I need to back off before something breaks

Do have coolant in the block...any suggestions?

Thanks

 

I believe the size of the square is 5/16", just so you don't round it out.

 

10-4... I even have a Snap-On square socket for the plug.

 

OK..got out today! Thanks...