Thanks for all your comments. I removed the stocks at lunch today and there is no pencil serial number. Nothing thin about these, but that is an interesting note. Do you think that was a marketing ploy by S&W? I figured they weren't original but, since this gun spent at least 30 years under my grandmother's mattress, they had to have been replaced very early on. Unfortunately I have no other information about the history of this gun as she passed several years ago.
I did notice today that I misread the serial number. It is 31xxx not 34xxx. Guess that makes it first change and maybe a year or so newer (since the first and second changes overlapped). I'm still getting used to the idea that I need glasses to read.
About this addiction thing. Does anyone know of a good divorce lawyer? I may need one soon.