So close to running, but then this happened!
I went through this last year. This is how I did it.
Here was the stud that broke:
This is the broken piece and the washer I used to weld to it. I used a fender washer with a smaller hole than the stud so I didn't nick the sides of the hole in the cylinder head:
Here is the welded washer to the broken stud. Then I just welded a nut to the washer and let it cool.
After filling the nut with weld and letting it cool, I backed it right out.
Good luck!!