It is my humble opinion that you need to take some extra steps to do it once and do it right...
You only need to remove the risers if there is a problem with leakage.
Find someone in your area that does cylinder head surfacing if you manifolds don't pass the straight edge test and get them flat.
On aluminum manifolds, I will either use copper gaskets or no gaskets at all, Permatex's Ultra Copper works well here...Again, just my personal preference...
It is also very important you use the proper torquing techniques, you have aluminum with a high expansion rate and iron, which does not (unless you have aluminum heads) so torque is vital to retain a good seal...Make sure the bolt holes are large enough to accommodate the bolt with little to no interference, the manifold is going to move, I don't care what you do...Do not overtighten and do not use lock washers, use hardened flat washers and star washers...
good luck!
GT
