On the passenger side of the 3rd member, there should be a stamped ID code. If you can post them, they can be decoded to find out what you actually have. I do agree that the one with the spring padns on the bottom is a '55 1rst, and the other is a '55 2nd-'59. The later rear can also be a 3.38 or 4.10 ratio, in addition to the much more common 3.90.
