Instead of buying a vinatge 10 speed and upgrading to indexing, you might just as well search out a late 1980s, near vintage, 12 speed that already has indexed shifting. Probably the three most popular Gran Touring bicycles during the late 1980s were the Miyata 1000, Specialized Expedition and Cannondale ST1000. The Cannondale frames were/are a popular choice for larger cyclists, though the oversize aluminum tubes and welded construction do not necessarily fit the image of a vintage ride.