Is there a book out there along the lines: A Field Guide to Mesozoic
Birds?
No, there is not such a book.
There is, however, a nice fat collection of papers on Mesozoic bird
systematics and evolution, with technical papers dedicated to selected taxa,
entitled _Mesozoic Birds: Above the Heads of Dinosaurs_, edited by Luis M.
Chiappe and Lawrence M. Witmer.
See also _Picture Book of Chinese Fossil Birds_ at
http://www.hceis.com/book.asp?id=777. I haven't seen this book in person,
but similar books I have ordered from China have featured excellent photos
of the fossils along with painted restorations (some more accurate than
others) and _very_ brief descriptions.