OK I'm back.
No expert here but the top of the frame is checkered and as far as I know the only S&Ws with that feature was the 357 magnums which became the model 27s.
Since the cylinder number matches the frame someone bored out the original cylinder to 45 caliber and changed the barrel.
At least that's what it looks like to me.
Not a collector gun but can still be a good shooter and it was your father's.