Is it possible that someone threw those 10" 1 3/4 in and they just happened to fit?
The backing plate seems to match the 68 to 70 one @Dana67Dart posted
Went to local parts store and they dont have anything in their system that would match the:
5x4.5
10" diameter
1 3/4 depth
I just comfirmed the large pattern. As far as I am aware the front disks only came in int 4.5 (big pattern) i tried my wheels and they fit both front and back, thus big...
I havent seen any chry co anywhere on the axle. I can try to get and get a PN but if you look back at one of dana67dart replies he posted a picture of a 67-68 backing plate and it matches basically perfectly.
I did not measure the diameter. I will be going back to the shop on Thursday i can measure it then.
Bolt patter i believe we discovered to be 5 × 4.5"
Does this picture help with the center of the axle?
Apologies for the delay. The car being at the shop is a pain.
So I counted and there are 9 bolts on the housing cover. I did my best with the pictures. As for numbers i couldn't find anything under there other than the tag with the numbers on the picture.