If your gasket is still in good shape, you can reuse it. I would recommend a good quality sealer for the gasket surfaces though. As for the manifold hardware....the ends should have studs that go into a water jacket. Coarse threads into the head and fine threads for the nuts. If the studs are in decent shape, I'd leave them alone. If they have to be changed, make sure you use some good thread sealer on the cylinder head end. The bolts are nothing special. Bring a sample to your local hardware store and find some grade 8 replacements. There again, coarse threads into the head and use some anti-seize compound on those since they go into a blind hole. The conical washer may be a bit harder to find, but, there should be lots of used ones out there if yours are missing or junk.