Greg,
The housing looks to be the genuine article and correct for an under ride car. The welds that join the tubes to the center look right. Despite having what looks like organic linings ( a common switch back then), they do appear to be 2-1/2 wide. It was obvious (to me anyway) in your first pictures that the diff had been out and painted and is probably about the time the shroud was left off. Nice find.
Randy