I agree to the above, but if you can not obtain a MotoGP system due to their limited availability, and do choose a Mac or other "production brand", then do yourself a favor and have it ceramic coated inside and out to aide in protecting it from corrosion and benefitting the system in scavenging.
I recently stumbled across this link:
http://www.c5ignitions.com/exhaust-kits.htmlAnd am planning to use this system for my BMW build to fab a custom 2:1 for my old airhead. It will be slightly easier than a 4:1, but if you prefer a 2:1 and a stockish look, you may have great success building your own.
But the MotoGP is the sweetest system on the market for the CB I've seen and beautifully made.