In general, engineering changes were and are indicated by a "dash-number" following the model number stamped on the frame. Sometimes model variations that were/are NOT engineering changes were so indicated. In some cases, minor variations were even indicated by model number. In the case of the model 60, I believe that the first real change indicated by a dash-number was in 1988, when the 60-3 came with the new large spring-loaded yoke screw. The 60-1 was a limited-production 3" SB, and the 60-2 was a 3" for the NYPD. Meanwhile, deletion of the pinned barrel, and a run with adjustable rear sights, both took place unnoted by a change in dash-number. This apparent inconsistency was and is typical of S&W numbering systems. I don't say that as a criticism, merely as a statement that their practice has not produced a consistency that some of us would prefer.
For all practical purposes, a no-dash Model 60 is simply a model 60 with the pre-88 yoke screw.