79 4x4 F150 Rear end questions

I just got a 79 F150 that has a broken rear axle shaft and I can't seem to figure out what size axle I should get for it. The PO of the truck used shafts out of a 90's model 4x4, but the passenger side slid out while he was driving down the highway!! The parts guys at my local part stores don't know what size shafts I am going to need, and neither do I.
*Is there some ID marks on the axle that can tell me what size I need?
*any measurments I can take to help?

I feel so stupid......[img]/phpBB/images/smiles/icon_frown.gif[/img]


But the whole thing only cost 150.00[img]/phpBB/images/smiles/icon_tup.gif[/img]
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Not sure if it would help but I thought the last year for 9 inch rear end was 1986. I would just call a salvage yard with a hollander manual and ask what interchanges. I know Ford messed around with bearing styles but on my 78 the parts store always came up with the right bearings just by telling them it was a F-150. Wouldn't think there would be to many axel types between 73 and 79, but I have read there are 28 or 31 splines.

The axle shafts are out of a 90's 4x4. Dunno how he got it to work, or maybe thats why one spit out on the highway[img]/phpBB/images/smiles/icon_eek.gif[/img].... But it is a 31 spline.. There is one axle that is a small bearing unit that broke and the recent one that slid out is another small bearing.... So now I am thinking that it is possibly a big bearing unit[img]/phpBB/images/smiles/icon_confused.gif[/img]
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