I've been tandem shopping. There are a ton of decent quality fillet-brazed Burleys and Santanas out there dying on the vine because they were built with 27-inch wheels and the "opposition" group of Suntour/Sugino/Diacompe, and in order to be brought up to code they need a new 700c tandem wheelset, cassette, derailleurs, and shifters, in addition to refresh with cables and wrap and seats, making the price for the project more or less the same as buying a much newer welded aluminum Cannondale or Trek that already has all that.