Sorry if I'm pulling out the ol' stick to beat on a dead horse.
I've done my research (searched the forums, internet, all that) and I think this will work, but I'd like to hear everyone's opinion on whether I've missed anything.
I have a 1983 Miyata touring bike. It has a 5-speed Suntour freewheel and friction shifters on the downtube. I'd like to upgrade to indexed shifting. I don't want to have to resize the frame and redish the wheel, and I want to keep the shifters on the downtube. Here's what I plan:
The spacing is 120mm, so I'll get an Ultra 6 freewheel from the Bay, which will fit in the dropouts. According to Sheldon Brown, the sprocket spacing is 5mm on an Ultra 6, which is the same as a Shimano 7-speed freewheel. Then I would get Shimano SIS downtube shifters (the ones where the rear shifter is indexed and the front is friction), a Shimano SIS derailleur, and a new narrower chain to fit the new freewheel. As long as the derailleur has at least six speeds, it shouldn't matter too much what I get as long as it's SIS, because I can just set the adjustment to not go past the last cog on the freewheel - the important thing is that the shifters match the derailleur.
So will this work? Is there anything obvious (or maybe not so obvious) that I've forgotten? How are the shifting characteristics of an Ultra 6 freewheel?