Observer:
As far as grips go, there are two different Detective Special frames. The original had a full-length grip tang (I guess that’s what it’s called) – the standard grips are flat on the inside and attach to either side of the tang like most Smith and Wesson grips. The newer frames have a shorter tang – the standard grips are mortised and touch each other at the bottom.
In other words, hold the gun upside down and look at the bottom of the grip. If you’ve got an original frame, you will see the two grip halves with the steel tang in the center. If you do this with the newer frame, all you would see are the two grip halves touching each other. (This is true when you’re looking at the original factory grips, some aftermarket grips may extend over or wrap around the tang regardless of its size.)
Unless you’ve got a pretty old gun, it’s probably going to have the shorter tang.