Those two numbers are out of the "Chevrolet Power" 2nd edition book, in the back. This was sold by GM as maninly an engine building rescource, but has susupension and body part numbers for racing use in the back of the book.
They are both listed as "5.312" length.
I have heard one other report where a number on my list for short arm was on a medium or long arm. I happened to have one the same number here, that was the short arm, so maybe there were mis-stamped arms or something?