BMW has a book called "BMW Coupes, A Tradition of Excellence. Part number 01 09 0 004 125, it covers all BMW coupes and as a bonus, comes with a reproduction of the sales brochure for CSLs. About $45 as I recall. Also, motorbooks.com or 1-800-826-4448 has the Brooklands book "BMW Six Cylinder Coupes and Saloons, 1969-1976" which is a collection of reprints of contemporary road tests from magazines of the period. It's $25.