Here are a couple of photos.
The first shows(L to R) the backstraps of J, K, and N frames. The second shows a K laying on top of an N, and the third shows the cylinder of a K next to that of an N. Both the K and N have square butt frames, and are fitted with standard "Magna" style grips. Larger profile grips-both factory and aftermarket-are available for both. L frames have the same size grip frame as well as grip to trigger distances as the K frame, although the rest of the frame is larger. As said, once you get use to looking at these, you can pick out the frame sizes from a mile away.
By the way, ignore differences such as the ejector rod shroud, as K and N frames are available both with and without these options depending on the specific model. Most(but not all) L frames and some N frames also have a full length underlug.
