If you're curious about the development of Oxcart as well as Area-51, check out Amy Jacobson's Area 51 book[1]. Appears like a solid detail of Skunkworks and spy plane history.

[1] https://www.amazon.com/Area-51-Uncensored-Americas-Military/...

I read a history of Area 51 that had several interesting stories in a similar vein. The book struck me as down-to-earth and well researched. http://www.amazon.com/Area-51-Uncensored-Americas-Military/d...