converting from stem shifters to downtube shifters - question
I just got an '85 Nishiki Riviera and I'm replacing a few components, learning about things as I go. I want to get rid of the stem-mounted friction shifters. Using clamp-on downtube friction shifters (also 6-speed) seems like the easiest option because it won't introduce any compatibility issues with the existing derailers and freewheel. Is that correct?
Also, I'm wondering about the diameter of the downtube. Is the diameter standardized, or does it vary among different tubing manufacturers (the Nishiki has Tange 900)? In other words, do I need to worry about getting a shifter mount with the same diameter as my downtube, or are they all the same?