Is there any major differences between S&W 17-2 and 17-3?
Not really.
According to the Standard Catalog of Smith and Wesson:
Model 17 no dash (1957) - Transition to model names from the old K-22
1958 - introduce 8 3/8" barrel
17-1 (1959) Change extractor rod thread, right hand to left hand.
17-2 (1961) Delete trigger guard screw, change cylinder stop.
17-3 (1967) Relocation of rear sight leaf screw.
17-4 (1977) Change to move gas ring from yoke to cylinder.
(1982) Eliminate pinned barrel.
(1986) Introduce 4" heavy barrel with serrated ramp on ramp base in place of Model 18.
17-5 (1988) New yoke retention system/radius stud package.
(1989) Model discontinued for Model 17-6, full lug version.
17-6 (1990) Full lug barrel with new yoke retention system.
Some early 17-6 reported without full lug barrel.
(1993) discontinue 8 3/8" barrel.
17-7 (1994) Drill and tap frame, change rear sight leaf, change extractor.
1996 Model 17-7 discontinued for introduction of 10 shot alloy cylinder version, Model 17-8.
1996 Begin shipments in foam filled plastic boxes.
1997 Ship with Master trigger lock, Change to MIM trigger.
17-8 (2001) Model 17-8 Heritage Series 6 shot with CNC new frame design.
17-9 (2009) Model 17-9 available as part of the Classic series introduction with internal lock, 6 shot cylinder with square butt frame, Patridge front sight with 6 inch barrel and wooden grips.