I hate to tell you this, but don't buy it. The 'Vette used the passenger rear, which is smaller. The spline count and axle diameter are the same, but the carrier, ring gear, and housing are much smaller. The '59 truck posi unit was a Spicer 45 from the GMC. In '60 they had an Eaton posi in the 9.375" rear for trucks, that was only used to '62/maybe early '63.
That would be what you would need to convert a '59 or earlier, but these are somewhat rare.
I have looked for one of these with little success. As far as truck differentials in passenger cars, the only production ones I know of were the "Black Widow" '57's. These were a special built cars for NASCAR racing, only 6 were built. It was common practice in the '50's and '60's to put a Chevy diff and brakes on a stock car for more durability, however.
