These bars were referred to as 'twin laterals' and were usually staight; nowadays tandems have a larger single tube there, referred to as an 'internal lateral' to supposedly add lateral stiffness.
Due to larger-yet oversized tubing, look for several new 2006 tandems that will eliminate any type of lateral tube(s) and actually be an 'open frame' design.
Pedal on TWOgether!
Rudy and Kay/zonatandem