I just had both of my exhaust manifolds off and successfully installed them with new gaskets. Like others mentioned, the studs tended to come out with the nuts. If you're able to, separate the nuts from the studs that came out as a pair. There were a couple that I could not separate and installed them together anyways. I was careful to make sure all studs threaded in an appropriate amount before final torque. Best practice is of course to thread the studs in separately until they bottom out and then install the nuts and torque to spec.

I did have issues with the exhaust shield nuts being seized. I ended up having to drill those out after the manifolds were off. I live in northern Alberta where rust is an issue. Hope some of this helps.