Old Fuff is dead on except for one thing.
In 1972 it became the model 15.
1972 should be 1957.
The stainless
Model 67 was also known as a Combat Masterpiece. There was also a .22LR caliber Model 18, which was known as the K-22 Combat Masterpiece.
The features that make up a Combat Masterpiece include:
Four inch ribbed barrel
Adjustable rear sight
Baughman Quick Draw front sight
Serrated front and back strap
You will note that these features, when first introduced, set an unprecedented standard for a .38 special revolver. The K-38 Combat Masterpiece was then (and is arguably still) the finest .38 special revolver ever manufactured.
The K-38 is simply a pre-1957 K framed revolver in .38 caliber. It would have a five screw frame. Here is a picture of my old K-38 Combat Masterpiece. It now wears a Hogue Monogrip, and is one of my sweetest shooters. I did a comparison between it and a Python
here.
K-38 Combat Masterpiece
The Target Masterpiece, by contrast, had a six or eight and 3/8 inch ribbed barrel and adjustable rear sight. Over the years, the front sight varied on the Target Masterpiece, but it was usually a Partridge type sight. The Target Masterpiece came in .22LR as the K-22 Target Masterpiece and later Model 17, and .38 Special to make up the K-38 Target Masterpiece and later Model 14. To make matters worse, there are also heavy lugged barels on some Target Masterpieces, as well as a K-32 Target Masterpiece/Model 16.
Model 17-3 Target Masterpiece
I hope this info has been more helpful than confusing........