They ride skinnier than they look. The rollout for the computer was almost three centimeters less. A fat two, anyway. And the bike felt quicker. So even though width and height seemed very close between the 32 and 35, the full cross section and volume on the smaller tire produce a tangible difference.
Meanwhile, a helpful reader sent me this link to a source for IRC Tandems. I haven't had time to research any of it further. I just know the tires disappeared from my parts suppliers' catalogs. Maybe this other site just has the closeouts.