>>>The other (only two built) Valkyrie
They built two and a half. Interesting story about the SR 3 being built from the long lead components of the third bomber, serving as the carrier for the Blackstar space plane.
http://www.aviationweek.com/aw/generic/story_generic.jsp?channel=awst&id=news/030606p1.xml
tlb—great info,thanks for the link.