It's an assembly number - nothing more.
There should also be a serial number on one of the grip panels.
You might want to contact Smith & Wesson about doing the work - the nice thing is that they'll mark it under a grip panel and you'll 'know' the work was done right.
As to the plated finish - do you know if your Dad had it done - or did he buy it that way?
At any rate, a nickelled S&W appealed to him, so having it re-plated might be the best course.
If you send a PM - I can tell you when the piece left S&W.
Vaya,
Scouts Out!