The biggest difference I have found is their weight. None of the pre-WW2 K-frames had the heavier barrels with the rib and full-length extractor housing. 38 special galley loads don't have that much recoil anyway, so the extra weight doesn't really help.
The second difference is the size of the grips. The small service stocks are harder to hold on to, for someone with big hands like me. It didn't seem to bother those early Olympic shooters, however!
Another difference is the very small adjustable sights, as compared to the sights of the 70's and 80's.
Mike Priwer