S&W used the same firing pin on almost all "K" frame revolvers of the same .38/.357 caliber.
Any changes were not between models, but between versions so you can use virtually any "K" frame .38/357 firing pin made during that time frame.
The firing pins are listed for the 65-4 as "pre-1988, and Post-1988". As far as I can remember, the pre-1988 firing pin was NOT spring loaded, the post-1988 has a spring under it.
Determine which type of hammer you have before ordering.
S&W calls the firing pin a "hammer nose" for some reason.
You might call them, they likely have just what you need and can positively identify which you need by the serial number of your revolver.
For a new pin and tubular rivet from the parts houses.
Brownell's. All parts are factory NEW.
http://www.brownells.com/aspx/ns/sc...mid=604&m=15&mn=Smith+&model=K-Frame+65/65LS+
They have both pre and post 1988 Model 65-4 hammer noses, part #24.
Hammer nose rivet, part number 26.
If needed, the hammer nose spring is part #61.