You can request a manual for free from S&W on their webiste, or download it.
It is not a J or K frame.
The S&W Model 64 is the Stainless Steel version of the "blued finished" Carbon Steel S&W Model 10 .38 special. Both revolvers are "K" frames. There are 5 frame sizes in the S&W revolver line up. The "J" frames are the smallest. The "K" frames are the medium service size. The "L" frame are a beefed up frame version of the "K" with a full barrel length ejector shroud. The "N" frame used to be S&W largest revolver frame. The "N" frame supports .357 Magnum, .41 Magnum, .44/40, .44 Special, .44 Magnum,and .45 Long Colt. The "X" Frame supports .460 S&W Magnum, and .500 S&W Magnum. Hope this helps with your question about S&W revolver frames.
If it is a large frame it's a 38 S&W If a small frame, a 32 S&W
K
it is a handgun made by S@W 38/357
K
N frame S&W Model number.
Medium
32
It is a J frame, the smallest. It is standard carbon steel. Also called the "Chief's Special."
the N frame is usually the bigger caliber as with 45, 44 and 357...........