Block Coolant Leak Repair???

[SeattleCarGuy]

Have an old 396 Chevrolet. Coolant plug above #3 cylinder where temp sending unit goes was rusted stuck and stripped. Used heat, broke an Eazy-Out, etc. trying to get the plug out. In so drilling, we got too close to the edge and removed some metal where the threads are so in installing the Temp Sending Unit, there is a gap between the sender and the threads which we filled with JB Weld. Well, it leaks letting some coolant seep out.

Next step is to remove the cylinder head and take it to machine shop for welding and install of helicoil.

Any other suggestions to save tearing the motor down? Any coolant sealer products out there that might work?

Thank you,

Paul