I can tell you that it doesn't matter. I've got 9-speed Dura-Ace bar-ends on my 7-speed Cannondale. I just put the shifters on friction, and they work perfectly. Shifting is so much easier with them, and they look alright. Just buy the 9-speed bar-ends from ebay, get them new in box, because they'll have all of the hardware you'll need, including routing pieces that go where the downtube shifters went to route the cable.
Here is my setup: