I have never heard of there being a different 10" drum between the 7 1/4" and the 8 3/4". 70 to 72 had bell drums and 69 back wasn't bell but they interchange. Maybe someone else can weigh in with more information on this.
My mistake, its the backing plates that are different between the 8.75 and 7.25. The drums are the same for both sbp 10" rears. (Thank you DrDiff for the info!)
Side note for possible searches...the small bolt pattern drums were used on 1973 through 1976 model year 4 wheel drum brake A bodies (mfg before 1/1/76).
