He is the answer. This is in the 70 Buick Service manual. Only two stamps were used in 70 for A body. CT is only one for drum. Same for power and manual. EA is disc. Can’t believe I forgot that was there
Interestingly Olds used the same CT code in 70 for drum but disc brake was different because Olds started using single bale master starting in 69 I believe. It is code EB and if memory serves me correctly 71 Buick disc was EB as well.