I saw a huge clue that it can be a service replacement, in the photo of the instruction sheet for the NOS valve:
This valve is shaped different than valve it replaces ..... and requires the new included brake lines for Fairlane / Montego, Falcon / Comet.
1967- 1969 Mustang / Cougar - Form existing brake lines to accommodate new valve.
I have 3 examples of what I call the 'Texas' shaped control valve. Mine all show: SURF 315-7 or (166-7, 088-5) X-2B328-BB. My guess is that the 315-7 is the Julian Date followed by the year? 1967 and 1975?
We mostly have examples of the C7OA-2B091-C and C9OA-2B091-A. No other casting numbers found. IMHO, I believe that the date code is year,month,day.
For C7OA-2B091-C, I found BA20,BE26,BK09,BL29,CA18,CA23,CA30,CB06,CG02,CG29,CK16.
For C9OA-2B091-A, I found JC21,JE08.