586-1 (1986) : Radius stud package, floating hand.
586-2 (1987) : Change hammer nose and associated parts.
These are the changes that were made seeing how there is a change in a years time...I would think the frame was marked -1 and the -2 changes happened while still at the factory so they restamped it to show the change. This is just a educated guess, could be wrong as it would not be the first time and not the last for sure.