I am looking to change the wife's bike to brifters. It now has Shimano 600 rear derailer. Can I still use the 600 or will I have to get a newer derailer. Another question is the bike had a 6 speed. Would I be able to move up to an 8 or 9 speed with that Shimano 600 derailer? This will be my first attemp at trying something like this. Is this something that a rookie mechanic can do?