I have an '81 with the MSD System.  My installation was part of the complete disconnection of the Chevy ECM.  I replaced the Chevy HEI Distributor with the MSD Distributor, Installed the Spark Box, and changed the exhaust system to Hooker Headers and a custom fitted, X-Pipe Exhaust (stock mufflers). I also replaced the carburetor and Intake Manifold with Edlebrock Performer components and just installed MSD 8mmm Ignition Wires. The car has never run better. It now runs and sounds like a Corvette is supposed to. Plus the engine looks nice and neet without all of the horrible plumbing and the ugly pump for the emission control system. It wasn't cheap, but it was well worth it.