From the Standard catalog of S&W, 2006 edition.
67 no dash = 1972-1977.
67-1 Move gas ring from yoke to cylinder. 1977-1988.
1982: Delete pinned barrel, no change to -1 designation.
67-2 1988-1993. New yoke retention system, radius stud, floating hand, hammer nose bushing.
67-3 1993-1998. Change extractor, rear sight leaf, drill and tap frame, Hogue grips.
1996: Delete square butt, no change to -3 designation.
1997: MIM thumb piece, trigger.
67-4: 1998-2002. Eliminate serrated tang, cylinder stop stud, New MIM hammer, internal firing pin.
67-5: 2002-2004. Internal lock.
67-6 2004- ? Two piece barrel.
The two piece barrel was noted for snapping off at the frame when fired. I think S&W went back to a one piece barrel around 2006, but I'm not certain.
