Unless his plan of attack has changed, he would epoxy it. In our case it came out, and locked the motor up on the return road 150 passes later. Took only 50 passes to figure out the original port work found a thin spot so we tore it down and sent the head back. I could write a novel on this painful experience, but here’s what I’d do. I’d try any sort of sealer. I’d probably try the GM tablets, or the CRC block sealer. Next would be to remove the head and look into any sealer/epoxy that could be flowed into the cooling passages.

Btw back then the car wasn’t 9 legal so my dad shifted at 5500 and was running low 10s. On one pass they shifted at 7200 and ran a 9.84 iirc. I think at 136....

Jay