The -2 just denotes the second engineering change.
The -1 (~1960) changed to a left hand ejector rod threading.
The -2 (~1961) eliminated the fourth screw in front of the trigger.
None of this has anything to do with the barrel length as you imply. If yours was shipped in 1980 it is a 28-2, just open the cylinder and look at the frame and you will see the Model number.
Click here:
http://www.handloads.com/misc/Smith.Model.Changes.asp