Your guns too early to be a transitional gun ,
The 15-6 and later versions did use that style barrel style but your frame was cut to mate with a tapered barrel.
Interestingly the older style 5 screw pre 1950 six inch K38 had a tapered barrel just like the 4" Combat Masterpiece and would actually mate up perfectly to your tapered frame,
A Problem existed in that the Model 14 and Model 15 had different frames and the Model 15 snub used a Model 14 frame.
So to simplify matters when the Model 14 and 17 got full underlug barrels they dropped the tapered barrel 15 and 18 frame style and used the Model 14 "Heavy" masterpiece frame for all K38/K22 versions in all barrel lengths.
Here is a six inch 15-6
now here is a four inch 15-7