Go to Smith and Wesson's website and request a manual. It's free.
The instruction manual from S&W that is provided with a gun is not a good reference for taking apart a 3rd gen pistol, especially if you want to go beyond the most basic form of disassembly called field stripping.
However... the 3rd gen pistol is not something to be messed around with unless you really know how the internal lockwork functions. It is one of the most complicated in terms of gun timing and relationship of parts.
Having said that... there are various videos on YouTube that are quite good for learning how to take down a 3rd generation S&W pistol.
You can also get information by joining one of the Smith & Wesson internet forums, the best one known, with the largest membership is smith-wessonforum.com
The Smith & Wesson Model 25-2, with serial number S283902, was produced in 1978. This model is a .45 Colt revolver and is part of the Smith & Wesson N-frame series. For precise dating, referring to the specific production records from Smith & Wesson can provide additional confirmation.
The Wesson part of Smith and Wesson.
S was not part of the Model 36 sn convention.
The Smith & Wesson Model 29-2 with serial number N64291 was manufactured in 1979. The "N" prefix in the serial number indicates it is part of the "N" series, which was produced from 1977 to 1982.
Aftermarket part
Smith & Wesson produced approximately 10,000 Model 647 revolvers. This model, which is chambered for the .17 HMR cartridge, was introduced in 2003 and is a part of the company's line of rimfire revolvers. Production of the Model 647 was relatively limited compared to other models, contributing to its rarity.
The Smith & Wesson Model 29-3, with serial number AVC 6797, was produced in 1987. The Model 29-3 is part of the renowned .44 Magnum revolver series and was manufactured during a period when Smith & Wesson was making various updates and improvements to their revolver line. For more precise dating, specific reference materials or production records from Smith & Wesson can be consulted.
The Smith & Wesson Model 66-1, with a serial number starting with "77K," was manufactured in 1977. This model is a stainless steel version of the Model 19 revolver and is part of S&W's K-frame series. The "66-1" designation indicates it is a variation of the original Model 66.
The Model 732, also known as the Smith & Wesson Model 732, was introduced in 1972. This revolver is part of Smith & Wesson's line of small-frame, double-action revolvers. It was designed primarily for personal defense and was chambered for the .32 caliber cartridge. Production of the Model 732 continued into the late 1970s.
The Smith & Wesson Model 13-3 revolver was produced from 1982 to 1988. This model is part of the K-frame series and is chambered for the .357 Magnum cartridge. It features a square butt design and is known for its durability and reliability in law enforcement and personal defense.
The condition of the gun plays a major part. For this shotgun, in 95% condition, the average is around $350.
The Smith & Wesson 64-3 refers to a specific model of revolver produced by the American firearms manufacturer Smith & Wesson. The "64" indicates that it is part of the Model 64 series, which is a stainless steel, double-action revolver primarily chambered for .38 Special cartridges. The "-3" denotes the third major variation or revision of this model, which includes specific design features and improvements made during its production run. The Model 64 was primarily used by law enforcement agencies and is known for its reliability and accuracy.