I'm looking to upgrade a low-end tandem (2002 Raleigh SC tandem) to something a little nicer without spending too much money, so I've been looking at the used options out there. I would want to upgrade the shifting on anything old enough to not have STI-style shifters. If I recall correctly, the cassette size should be about the same for anything in the 8-10 speed eras, so an 8-speed system could be upgraded to a 10-speed system without changing the wheel (someone correct me if I'm wrong). I recently found a 7 speed Burley Duet (the seller says it's a 1993) and I wondered whether anyone knows what dropout spacing to expect on this bike, or others from the 7 speed era. Is it likely to fit an off-the-shelf mountain bike wheel?