Use a good quality steel,stainless,or even silicon bronze, for the studs, bolts. You need the tensile strength. For the nuts you can use a good quality brass. Good luck finding that. Stainless nuts would be my choice with a good high temp anti seize on the threads. Make the nuts the sacrificial part and it should be good for many years. Studs and bolts are hard to remove when stuck. Nuts, not so bad. Never ever put manifold on with out anti-seize. EVER! As you can tell this has been covered pretty well. Brass and stainless will gall and the use of anti-seize will help that. Galled stainless is a b!@#h to remove. Galled stainless nut on a stainless bolt? A disaster. both will be destroyed.
