The Stovebolt Site Forums The Shop Area Driveline 1958 apache, rear differential identification

Here's the manual section on the Positraction equiped axle for '59.
Something that should be noted, the terms "posi" or "positrac/positraction" tend to get used far too often as a generic term for limited slip, even when referring to a non Chevrolet axle. Positraction and Positrac are Chevrolets sales terms for a limited slip differential.