Stainless bolts, and coat them with Neverseize. The stainless bolts won't corrode and are probably about a grade 5 bolt. I wouldn't use grade 8 bolts as they tend to get brittle in a high heat application and can just snap off after a while.
The retainers/locks can stop the bolts from loosening during the heat cycles expansion and contraction.
The steel shim gasket such as the factory used is pretty durable until the bolts loosen, then they develop leaks. I would check the mating surface with a straightedge to insure the manifolds are flat, they can be surfaced if they aren't flat.
If you want to add some insurance against future leaks coating the steel gaskets with high temp RTV will add some extra sealing ability. Apply the RTV and let it skin over for 20-30 minutes before assembly.
Have fun...………..
