Best way to go about this?

Fixing to do a service and the cam tensioner, one of my header studs broke. What’s the best way to get these replaced? I was thinking of welding a nut, but I’d like to hear your opinions. They are really rusty and I’m expecting the same thing for the other header. I’m doing a small refresh on the bike, including new headers and piping and I’d like to get these changed to avoid the headache in the future.

Any help is appreciated, thank you.