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Your rear axle should be a Ford Sterling 10.25". The C6 is a 3speed auto with no overdrive. The E4OD is a 4speed auto with overdrive and it has an overdrive off button on the end of the shift lever. It was used behind small blocks, big blocks, and diesels. The AOD is also an overdrive 4speed auto used behind small block engines. I would think the engine would be either a 351 or a 460 and the trans would be either a C6 or an E4OD. I have not seen an F250 with a 302 or an AOD trans, but that's not to say they don't exist...
Look on the sticker on the drivers side door pillar. Some of the codes the VIN number the 4th position is gvwr H is 8501-9000, 8th is engine N is 302; H is 5.8; L is 7.5. On the sticker on the drivers side door pillar, trans K is C6 auto, T is AOD. Axle for over 8500 gross C5 is 4:10 LS ;C9 is 3:55 LS; 38 is open(not LS) 3:08; 35 is open 4:10; 39 1s 3:55 open. At least that is what is in the Ford shop manual.