From his comment, it sounds like the bike is still OEM - 27" wheels, non-index Sun Tour 6-Speed (18 speed triple!), having been in storage much of the time since purchase. He also asked how the bike was for touring. It was fun writing the reply:
Yes, we have ridden our Sovereign since we took delivery in 1985. It is currently in its third iteration, after being converted to 700c and Sun Tour Index after the first 10 years, and then converted to Shimano 7 speed in 2008 (you can follow that adventure here http://thinktandem.ning.com/forum/topics/2129999:Topic:12 ). I updated the front stem and handlebars in 2009. I am looking for a replacement for the cranks and a possible change to 10 speed in the next year or two.
Our Sovereign has over 28,000 miles on it. That includes over 3,000 touring miles (we had another 3,000 miles of tandem touring on prior tandems), another 2,000 miles with a Kid-back, and 2,000 miles pulling a Burley Trailer with a child. It also has 27 centuries, 1 RAIN and 1 STP. I am posting a lot of adventures and experiences in the coming months at www.thinktandem.info.
It has been a good bike and is almost part of the family.We may have kept it too long for avid riders, but on the other hand, we made some career and family decision for our kids that let us stay avid riders. All in all, it was a fair trade.