I've been using a 1986 Bridgestone 300 mixte to commute for about a year, and have decided to upgrade to indexed shifting on the rear and add bar-end shifters. I added traditional looking upright-style Albatross handlebars when I started commuting. The bike currently has 6 gears with Shimano light-action derailleurs and stem shifters. It's my understanding that I will need to replace the rear derailleur and the shift levers and use longer cables. I don't know where to go for these, or what I should look for. Are there good vintage choices on eBay, or do I have to go new? In either case, what models would be good, and what's the likely cost?