1956 Ford or Chevy Rear End??

Hi,
In 1969 I built a 1937 Plymouth street rod which I ran for a few years and then parked it. Now I'm rebuilding it.I was sure that The rear end I used was from a 1956 Ford. Even talked to the person who gave me this rear. He said that was right. While sandblasting it I came across these numbers on the front.

D56
3707306 GM 9
The GM is in Large letters.
So is this a Ford or Chevy Rear?
Also it is 60 inches axle flange to axle flange.

5x4 3/4 axle studs

Thanks, Barry

Right off the bat, the 4 3/4 would be GM, Fords are 4 1/2

Just so happens that carrier casting # is from '55 Chev.......fits all the way up to '64 Chev.