Kelsey Hayes Disc Brake Upgrade Question

65 Cuda 340 said
. (I'm thinking these might just be the standard nine-inch brake wheel cylinders, but I don't know that

Their ad says they reduced the id by 13%

9 inch has of 0.594 (per RA)
10 inch has 0.906 (per RA)

13% of 0.906 is a little over 3/4" so bigger than 9" and smaller than 10 inch