I am upgrading the brakes on my 1970 Dart that came with 9” manual drums. I have acquired and restored a set of original K-H brakes from a 1969 Swinger 340. I am about to button everything up but I have been reading about brake proportioning. An aside: My neighbor’s father-in-law had a Duster with a power K-H system. That car was a 318. He says that you breathed on the brakes and it would try to launch you through the windshield. I just want to make sure that the 9” rear drums are appropriate. I have not heard of 10” drums for a 7 1/4” axle. I just don’t want the rear end to swing out in a panic stop. Thanks.