>>>There was a small little adapter that would let you use the regular
shifters on the top of the down tube. I have one but it is ear marked
for a frame I have. Steve<<<
>>>Do special top mount shifters exist? I've thought the top mount braze
ons accept common down tube shifters.
http://home.t-online.de/
Besides the top-mount boss pictured on the link, there are at least two (maybe more, but I know of at least two) types of braze-on mounts for top-mounted shifters. I think these were designed specifically for top-mount shifter assemblies like the Suntour Symetric and others. They (the braze-ons) consist of a single, threaded semi-cylindrical boss. My '83 3Rensho is so equipped, and it came outfitted with a Dura Ace top-mount shifter assembly (I hadn't seen one of those before either), part of the first (7400?) 6sp indexed DA group. I wanted to outfit the frame with Suntour components. While the Suntour Symetric system fit the boss, I wanted to use conventional Superbe Pro shifters. After finally scrounging up one of the little adaptors Steve mentions above, I found that it would not fit the braze-on. The braze-on was too long longitudinally for the adapter. I had to file down the fore and aft edges of the braze-on, ultimately making it sort-of a square with rounded corners, before the adaptor would fit. It wasn't terribly difficult, and the adaptor now fits, but the adaptor was definitely made for a different braze-on than the one on the 3Rensho.
So when you are hunting for these bits, just be aware that one size does not fit all.
Wayne Bingham
Lovettsville VA