I have a 9" Ford rear end/third member and it has a larger longer pinion shield with a rubber snubber on it.  It is larger/longer than the one on my 57, which does not have a snubber.  It looks like it is stepped up to miss the drive shaft.  I think the 3rd member is from a 57, it is a 3.89 ratio.  I can't count the splines, I assume there are 28.  Do some 57's have different pinion shields? or is this not a 57 passenmger car differential?

Paul J. - '57 E Code