Well, it's not the 1950s variant, but it still looks pretty cool. I have a GB stem from the 70s with longer reach, if that might help. Let me know, Rudi.

In terms of tires, Kenda still makes a 597mm BSD tire (Schwinn S6 size):

http://www.sheldonbrown.com/harris/tires/597.html

Here's the 1962 catalog entry for the "Lenton Convertible." No additional specs listed, unfortunately.

Neal