From what I have been able to tell it's the Eaton rear end with the round cover, still need to clean the gunk off to get the part number off the housing. The Corp. rear end has similar innards but a different shift motor mount and elongated cover, so I'm relatively certain it's the Eaton that was available from 55-57.

1956 GMC 370 dump " 'Tater "
1970 VW Volksrod "the Black Bomber"
2007 Chevy Avalanche
2020 Jeep Cherokee Trailhawk,
2005 Harley Davidson FLHTCUI

I dig all cars, old and new, whether they were hammered out of American iron, German steel, or Japanese tin cans. Being unable to appreciate them all is missing out on a world of great things.
But thats just MY opinion! :P