I purchased a copy of this document a few years ago and while the Boeing Model 448 was already included in a lot of books on the B-47 with respect to the history of design and development of the B-47, many of the bomber designs in this publications had only been previously covered in news journals or otherwise remained cloaked in secrecy until researchers got the chance to take notes on those proposals after the archives were opened. The inclusion of the Vought SLAM nuclear-powered cruise missile in the document is problematic because the SLAM wasn’t a bomber but instead a cruise missile despite carrying a nuclear weapons payload. With respect to the D-436 proposals that constituted the first phase of North American’s design studies for the AMSA competition won by the B-1A, research by the late Robert Bradley in the 2010s confirmed that North American Aviation had a D-series design number sequence separate from the company’s NA-series company designation sequence, in which case the D-436 designation was part of the company’s D-series company designation sequence (the X-15 bore the internal designation D-250 whereas the delta-wing X-15 project was internally called D-435-1-4). 

As a side note, the first issue of US Bomber Projects notes in the preface that Scott Lowther shelved his planned “magnum opus” on post-World War II US bomber projects, US Bomber Projects Since WWII, long ago after he realized that such a book would not be a financially cost-effective publishing project due to several authors coming out with books covering many aspects of the scope of his planned book US Bomber Projects Since WWII, including the initial and revised editions of Tony Buttler’s American Secret Projects volume about bomber, attack, and ASW aircraft as well as Jared Zichek’s book on carrier-based strategic bomber designs for the OS-111 and OS-115 requirements by the Navy (the Douglas D-593 won the OS-111 contest and became the A3D, but the Navy shelved the OS-115 requirement before it could evaluate the Douglas Model 1186 or any other OS-115 design submissions and decide which one should be selected).