Garage space has been tidied up since I took this picture

A friend of mine has a ‘95 NA Miata. It simply needs the exhaust system re-attached and it’ll be roadworthy again. We’re calling on Oppo for some advice on how to go about it.

As of right now, the manifold and related parts aren’t connected, but we want to replace one of the damaged studs for the exhaust manifold gasket:

The offending component

What’s the best way to remove one of these? Here’s a picture of the engine bay for reference:

Any and all advice is appreciated, I’ll be documenting the build across the course of this week. We’re taking it slowly so far to make sure it’s done right. I can take more pictures if needed, too.