While replacing the studs is obviously the main goal here, keep in mind the main problem to focus on is the manifolds are warped. So if you only replace the studs, and you reuse the old manifolds(without fixing the warp), you’re setting yourself up for failure. When you torque the old manifolds down, you’re putting a BUNCH of added stress on the studs(manifold bending). I would suggest taking the old manifolds, if they aren’t too rusted and in decent shape, to a machine shop and have them decked. I wouldn’t trust new manifolds without doing the same process. Moreover, new manifolds still need to go through a few heat cycles to fully relax to their final state-meaning you could deck new manifolds, but they may still flex after they get heat in them. Which is why I suggest using old manifolds and get them decked.
If you have a big enough table top belt sander, you can do this at home. It’s not perfect, but if you take your time, any variance is well within the gasket thickness, not to mention wayyyyyyyyy within a warped manifold. Food for thought.
