Hmmm, looks like barend shifters were the only 600 bits on many of the '90s 520s. Are there other 600 bits on it? Of course nearly 20 years leaves plenty of opportunity for parts swapping.
A 1992 will have a sans-serif font where as the 2003 has a serif font for the Trek Logo. 1992 has model # on the seattube, 2003 is on the top tube. 1992 top tube will be horizontal whereas the 2003 is sloping.