help with rear end identification

[billo92]

so i bought this 1958 step-side short-box apache. when i took off the rear drums they were filled with diff lube so i knew i was gonna have to replace the axle seals. but when i got the diff apart i found a ton of wear on the carrier pin (which was causing a ton of slop/play in the pinion). so i started trying to figure out what rear end it was so i could hopefully get some new parts for it. well.... its a 10 stud cover, with a drop out third member (also 10 studs) the ring gear is 9.5 inches diameter across the middle (im not even sure if thats the correct way to measure the ring gear, because when i measure straight along the open edge of the carrier it measures 8.5 inches exactly, which is of course a common 10 bolt gm size?) the ratio of the rear end is 3.90:1 (39 on the ring gear 10 on the pinion gear) so i went online to try and find anything out about this rear end and i cant find anything about a 10 bolt 9.5 inch 3.90:1 ratio rear end or anything close to it. this is a problem because i cant find parts until i know what i need. if it helps the ring gear is held to the carrier with 12 bolts and the axles are 17 spline. oh, and the ring gear is stamped "gm" and then a part number and the gear numbers 39-10 and its non posi.

any help as to what rear end this is and/or where i can find replacement parts for it is greatly appreciated. thank you!

bill