It is easier to find cheap BMW factory manuals for the pre-1970 bikes because they are available as copies.
Here in the Huggett Online Shop you can buy an original quality manual:
01 51 9 798 461 Workshop manual R60/7- R100 RS >1983, GB = English, for about $100.
Or perhaps one of these might be all you need:
Clymer Manual
BMW R50, R60, R65, R75, R80, R90, R100, R100GS PD Repair Manual 1970-1996
This repair manual covers 1970-1996 BMW R Series Boxer Twin models, with 500-1000cc horizontally-opposed engines, with pushrod-operated valves, including:... R60/7 1976-1978
Item # M502-3 $31.22
http://www.themotorbookstore.com/bmwrser19.html
Haynes Manual
BMW R45, R50, R60, R65, R75, R80, R90, R100, R1000 Repair Manual 1970-1996
This repair manual covers... R60... 1969-1978
Item # 0249 $29.72
http://www.themotorbookstore.com/bmwtwin19.html
Also from:
Amazon.com
http://www.amazon.com/Haynes-Motorcycle ... 1859602835