If you can swing it, Stage 8 fasteners make a kit that locks exhaust hardware down through the use of fancy bolts that accept a lobed washer and an E clip to retain it. It's excellent for headers. They also make hardware for the flange. It's been three years, and I haven't had any leaks after snugging everything up after a hundred miles or so in my truck. I did buy fancy reusable manifold gaskets as well. Absolutely worth the extra cash in time not spent chasing stupid header leaks. If you've got all studs and nuts without bolts, find copper nuts. They won't seize, or back off as easily as regular hardware. If they do back off, or your money is more dear to you than your time, you could always drill and safety wire everything to keep it in place. I've got a couple of cars like that, as well. Oh, copper anti-seize works pretty well, also.