Olds/Pontiac http://www.jalopyjournal.com/forum/showthread.php?t=129676&highlight=olds+pontiac&page=2
not earliest 50s, more like mid 50s with those swaybar brackets. IMO It won't be a posi in pre-57 likely ratios are 3.23 A/T and 3.42 std trans, for mid 50s
That rear end is an Olds/Pont, POST 56, and is most likely a 57 or 58 housing with that 3 ribbed third member, if it's original. Probably going to be 29 spline axles, and that will definitely tell you the year (57-58). 59 on used 31 spline axles, and those rear ends were 1 inch wider per side, as were the axles. You can usually just cut 1 inch off the longer axles and slip them in the 57-58 housings to use the more common 31 spline Positraction; the only 29 spline Positraction was only in 58, and are quite rare nowadays. Sometimes, the splines need to be extended when the axles are shortened. Butch/56sedandelivery.
It's hard to tell in your pix, but the pig will be perfectly round if it's a '57/'58. '56 and earlier are slightly oval shaped. If it's an original, untouched rear, the best way to tell is by the axle splines, casting date, and casting number. '57/'58 originals will have 29 spline axles, while '56 and earlier will have less splines. Facing the snout head-on, the casting date (alphanumeric where A=Jan and L=Nov) will be located at the five o'clock position where the pig bolts to the housing. The casting number is located at the nine o'clock position. I can see the raised numbers of the casting number in your pix. A stamped digit indicating the gear ratio is likely there, too.
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