I was trying to measure the brakes from the ground under the car. Again thanks for the information. I haven't had any luck finding a salvage yard with pre-90's anything.
The diameter should be stamped on the outside of the drum somewhere, usually as a "max 10.090" for the maximum serviceable diameter. The backing plates are also about 1" larger in diameter than the inner diameter then the brake surface, so, 10" drums would have 11" diameter backing plates.
