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You have a Dana 60. A pretty much bullet proof axle with it's 9 3/4 ring gear. Even stronger than a 9". You can get any gear ratio you want from 2.xx to 5.xx (x meaning numbers).
I know for sure they were used from '56 and up on the F-350. They may have been used on 53-56 F-350's. Sounds like you have a F-350 since the frames don't have a frame arch over the rear axle.