The actions of the 602 and 550 are the same (dimensionally speaking).

The subtle differences are:

1) safety
2) bolt shroud
3) trigger
4) finish (the 602s have a bead-blasted blued receiver and look similar to a pre-64 model 70 finish)
5) stocks are much slimmer on the 602s

Other than that they are the same, but I (like most others here) prefer the 602. Primarily for the slimmer lines of the stock, i.e.: a good friend has a 550 and it is a little "clubby" compared to my 602 which is "trimmer" and quicker handling.

Mine was made in '92. The earlier made models of the 602 had an optional peep sight.

Do a search here. There was a pretty comprehensive history given of the 602 recently.