Hi GeeVee, I've just checked out your pics. Nice truck! Is that a metal tag on the rh side of the diff cover?
If so it may have the Info your looking for.
I fitted an 86 Firebird axle in my '50 and the tag has the orignal GM part # and diff ratio stamped on it.
I hope this helps.
Jock.

1950 Chevy Advance Design 3100 in Scotland
In the Stovebolt Gallery
More pix on Flickr.
I've definately got this truck thing in my blood ... my DNA sequence has torque settings
"Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.