Okay - a few comments here.
First, I'm sorry for your loss. I, too, have lost a brother.
Second, S&W never called any of its revolvers a "Police Special." Mostly likely what your brother carried was a .38 Military & Police Model 10. If you open the cylinder and look on the frame in the yoke cut, you'll see the model number as MOD 10-x. Very likely it is a Model 10-5 or 10-7, but it could be some other dash number. That's assuming it holds six shots.
Again, assuming a six shot cylinder, it will be a K frame size. The correct stocks would be the K frame "PC" (Plain Clothes) grips, properly called Modified Magna stocks. They will be checkered and will lack the smooth diamond around the grip screw.
The number in the yoke area has no meaning. The serial number you need is on the bottom of the grip frame. Very likely it will have a letter D in it. It could be a C, but if your brother was on the force in the 1970s, a D is more likely.
I'll include some photos.