Many thanks to all on the list for their helpful replies re. my stem and bar dilemma! I learned a lot. The GB Bibi stem was stock for the Raleigh Competition GS so that's a keeper; the specs called for something called a Raleigh Italianate bend or what must be a generic alloy bar. So the hunt continues.
Now if I had just consulted all of you before I foolishly bought this machine on eBay in the first place....
Peter Kohler
Washington, DC USA