That BA Dual Bail master cylinder was used in 1969 in front of a 9 & 1/2" Booster.
Brake Booster assembled on 3199=1973-199th day.
LR=
...I've only seen 3 or 4 digit #'s here.
<u>Horns</u>
9=1969
D=April
5=day
2=1972
C=March
9=day
Delco #9000...#279 Lo note & #280 Hi note are correct for GM A-Bodies.