That is a 1957 Chevrolet rear end. It was the ONLY year with a drain plug. The 57 also uses different/larger axle bearings, so you need to know that for any future axle/bearing work. Gears were 3.55 with an automatic transmission, 3.70 with a 3 speed manual transmission, and 4.11 with a manual transmission with a Borg Warner overdrive. There are LOTS of different gears both from Chevrolet and the aftermarket however. The third member will swap with any 55-64 full size Chevrolet Car, 62-64 Chevy II/Nova, and 56-62 Corvette. Looking directly at the third member from the front/U-joint, if it's a Positraction case, it will have a large "P", although 57 was the ONLY year that DID'T use that identification method. Could have had a lot of things done to it over the years. 8.2 inch ring gear, and should be plenty strong, unless you really beat on it with sticky/big tires.