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.
That has some correct information.
Yes there were /6 equipped B-bodies that used BBP rear drums with 1x1.75" shoes.
Drum p/n 2534 173
Shoe & lining package for all 4 brakes was unique because of the combination.
Rear wheel shoe & lining package was the same as A-bodies
(1967 Parts Book)
Whether those finned KH are for Chrysler or another manufacturer, I don't know.
KH made OEM and aftermarket parts for all of the manufacturers. For example Ford also had a 10 x 1.75" rear drum. Shoes are virtually the same, but aspects of the drum are most likely different.
Here's an example of the SBP version - aftermarket, IIRC Wagner.
Sorry I don't have an inside view
There was also a version with wider flange or lip that sometimes shows up for sale. Pictures here: "Bell" style drums
Here's Centric's dimension's for the SBP version. For the BBP should be the 4.5" bolt pattern and probably 1/2" holes for wheel studs.