AB stamped 5452310 Master cylinder

[sabino56]

Hi,
I have a 68 base coupe with drums all around.  I pulled the master cylinder to rebuild. It's a 5452310 which I understand is the right MC for this car.
I read in the research that 68's with drums would be stamped BS with possibility of some with CT. Mine is stamped AB. I don't see it in table in the research.
It has a 275 which I think is Julian date for casting - Oct?  but I don't know how to tell what year.  It also has a faint 281 on the machined surface for the front brake line port. 
I've had the car since 74 and don't recall replacing the MC but can't be 100% sure.
What applications used "AB" stamped 5452310 MCs? 
Thanks for advice
Ed

[bertfam]

I believe the AB code was used on 1967 through 1970 full size cars with 4 wheel drum brakes, but Kurt might be able to verify this.

Ed

[sabino56]

Thanks.
I took it apart yesterday.  It does not have the RPV / check valves. I bought the car in 74 so I must have replaced the MC at some point and forgot.

I read on another thread here where you said the 281 stamp would be the assembly date and the 275 was the casting date.  Is there anyway to know what year?
Ed

[bertfam]

Not unless it's in the stamping. Sometimes they're stamped with the last digit of the year then the Julian date (i.e. 7281 which would be October 1st, 1967). Yours looks very light so if the year is there, it'll be difficult to see. Try shining a light on it from an angle or using chalk to highlight the stamp.

Ed

[sabino56]

Looking closer there is another digit - at the end.  2818
Reading it sounds like the year can be before or after the julian date?  - so this would be 281 of 1968, I think.

[bertfam]

Yes, sorry. The year is AFTER the Julian date.

Ed

[firstgenaddict]

281 would be correct for the machining and assembly - the 275 in the underside is the casting date - in Julian format- totally lines up.