What type of management system would one need in a '99 m6 to run a 427 Gen 3/4 motor and make around 600 to the wheels?

 

Stock PCM will work. That's what Lingenfelter uses on their builds as well as the ZL1 Camaros built by Berger/GMMG. You'll either need to find someone to tune it or pick up a piece of software (EFILive, HPTuners, etc.) and learn how to use it. I suggest option B if you have a little patience and love to get your hands dirty.