cyclotoine

I don't quite understand what you are asking.

You have a braze on for top mount shifters (aero shifters) on your nishiki? Both shimano and suntour made them where they bolted on via a single 5mm bolt into a bottle type braze-on on the down tube (as seen above). There were also bikes with a sort of plate with brazes ons for DT shifters brazed onto the top of the DT. You best bet would be to find a set of "aero" DT shifters and see if they have standard fixtures which you can mount your 600 levers too (if you frame has the same type of mount as the Colnago above, which is what I am asuming at this point). Hope that helps.