Just curious, given a Shimano Dura-Ace 8-, 9-, or 10-speed downtube shifter, could you make it shift one of the other number of speeds by changing just the SIS unit?
This Shimano tech doc for 7700 9-speed or 8-speed* downtube shifters looks a lot like this one for 7800 10-speed levers. I'm no mechanic, but it looks like the SIS units are interchangeable, and you can buy them here for $30 - $50.
*I thought 7700 was only 9-speed, so I'm a little confused about the tech doc saying 8-speed.
I don't plan on doing this, it just crossed my mind that it might be possible.