Index shifting for Old Schwinn Twinn?
I bought an old modified Schwinn tandem late this summer to see if we like tandeming, and the good news is that we do! The tandem we bought is a 1970 Schwinn frame to which someone added 10-speed capability. While I am able to shift without indexed shifting, it's too much for my wife and daughters, and I'm wondering if I can add index shifting to this bike.
I don't know if the rear derailleur is original -- it's a SunTour AG -- tied to a 5-gear cassette that ranges from 14 to 38 teeth. Currently there's a flat bar handlebar on the front that looks like it came from a kids BMX bike, but ideally I'd also like to upgrade that to something like my Trek hybrid. Thus grip shifting would be nice, but not necessary. One thing that might cause a few chuckles out there -- the shifters are currently mounted on the stoker's handlebar. I've never seen or heard of that before!
And here's the cherry to top it off: I can't put much money into this, so replacing the entire cassette and derailleur is not an option.
Any thoughts? Any additional info that would help?