3alarmer 

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...you are talking about two different things in your question. One is getting the shifting up off the down tube, which is pretty easily accomplished using either Suntour or Shimano (or maybe even Microshift) bar ends. The other is a conversion to indexed shifting, which is going to be more expensive, and somewhat more complicated. At a minimum, for indexed shifting, you will need to replace the rear derailleur to something with some float on the top pulley wheel. IIRC, the spacing with five and six speed freewheel cogs is about the same between the cogs, but as others have pointed out, bikes made and sold with 5 cog freewheels mostly had 120mm rear dropout spacing. Six and seven cogged frames are spaced at 126mm.

You don't really get more gear range with more cogs in the back. For my needs, a touring bike is all about gear range overall, not the number of gears from which you have to choose. Most of my touring bikes are set up with a triple in front, and a reasonable rear cog selection that goes from about 14-28. I guess if you really need brifters to be happy, you might be able to scare up some used that will sort of work, but they will likely be older and in questionable condition.

For total gear range and ease of use, it's pretty hard to beat Suntour ratcheting barcons with a triple in front, the small ring sized as a granny gear. But you'll probably need a different crank or a tripleizer ring for that, as well as a new rear derailleur with a long cage to take up all that slack in the chain. That's more ooor less what I have done for my own riding on bikes of the same age as yours.


Edit: I see now you mentioned it is "an old Nishiki touring bike", so you might already have a triple crank and a rear derailleur with a long enough cage. In that case, find some Suntour barcons used somewhere and try them out as your first step. It's a minimal investment, they work well, and they might be enough to solve your problem. Brifters are a mixed blessing for touring, because if something goes tits up with them, they can be difficult to repair on the road. Suntour barcons are pretty bombproof, and the cables are easy to access for replacement.
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