clean the area with brake kleen/let it set up 24 hrs/cross your fingers/get the "regular" type not the fast setting.
What I did was use the slow acting. I cleaned the area with brake clean, let it set then applied the JB to the tab. Placed it into position, put the stud back in, tightened the nut, let it set for about ten minutes. I then backed the nut off so no pressure on the tab. This morning I removed the nut and stud, placed some sealant on the stud and installed it. Ran the nut on and torqued to spec. I'll let it set for another 24 hours to allow the sealant to set before I fill the rad and burp the motor before I fire it up.
I have a buddy up in WA State that's a retired pipefitter who is expert at welding cast iron. This summer, I'll pull the manifold and get it up to him.
Probably in the future when using old cast iron manifolds and other parts is to have them magged to insure there's no cracks. As clean as that break was I'm sure there was a hairline crack.
