Art,
You are correct about the C9M6015. It is a 1969 Mercury enging but most of the Ford line has a number such as C5ZZ-2140-CR.
C5==1965, Z= car line, in this case Mustang, Z= Ford service part, This came from Ford enginering department. The 2140 is a basic part number which in this example happens to be a master cylinder.
Is yours a big block or small block and did you maybe miss a letter code between the M and 6?
Another person posted his number for his block and it was E9AE-6015-AA-9. That breaks down into E= 1980s, 9= year, ( 1989), A= Galaxie, A= Ford engine department. I am sure some of the guys have a btrakdown for your code but everything I have or have seen has CXX-XXX type code.
Try this link
WWW.ac427.com/html/engine_numbers_ford.htm
Also this one
www.classicmustang.com/decoding_part_numbers.htm
Also
http://pliverman.home.mindspring.com/index3.htm
Hope this helps.
Ron