I do not know if NAPA has the gasket. We have re-installed used ones with no problem using high-temp RTV if the gasket is not damaged and the mating surfaces on the manifold and turbo are clean and flat. We find it works best to run a small bead of RTV around the gasket on both sides and let it set up before assembling. This way you get a very good seal without the typical oozed out material like you get with RTV that is not set up.
We loosen any stuck nuts with an acetylene torch, heating the nut to red heat, then letting it cool a bit and then removing it.
We have changed out many turbos experimenting with the power out put of the different ones. As was said, when you have done it several times, it takes about 30 minutes. Anyone with a good mechanical skill level can do it easily.
Regards Marti