New Kelsey Hayes 10 x 1.75 brake drums with BBP??

Every online reference I can find shows that 73+ A-body was 10 x 2.5" with 4.25 bolt pattern.

I just had a fella from another site PM me that these drums are for 66-70 B-body with /6 and 7.25" axle and have been discontinued for decades, unable to confirm though.
Ok. Then keep reading them resources.