In 1987 S&W made what was called the model 19-P. Think of a model 13 revolver with a 2 1/2" or 4" model 19 barrel. The front sight ramp was milled down to make a very low, small ramp and blade, somewhat like, but not exactly the same as one on the model 13. They were intended for export to a South American country, although some ended up in Europe. Why they didn't make a 2 1/2" model 13, I have no idea, but maybe the customer wanted the model 19's underlug.
Elmer is right. You will have to change the extractor rod and center pin. You will also need a good gunsmith with a milling machine to make the new front sight.
A lot of work, but yes it can be done.