I have a 1987 Peugeot Versailles. I want upgrade the wheel set. It has a 7 speed shimano freewheel cassette. I have a used set of Mavic Open Pro 32 spoke with Ultegra 6500 Freehub. The bike has Shimano 600 down tube shifters. What do I need to purchase to make this conversion happen? Any help would be great.