Well, if you're in "this good a condition" at an advanced age, you're going to be a lot like me----everything works (more or less)---nothing's really wrong enough to fix---you'll be too fat----have a pretty fair bunch of wrinkles, and you won't have near as much hair as you used too. It'll be pretty much like this gun, where you note the finish "has some issues".
So, all things considered, you could be a lot worse off. The bad news is the value of your gun is based almost entirely on what you can see----the finish----the more the better. Based upon the photos, there's not much left---and none at all on the trigger and hammer (which is going to catch the attention of pretty much anyone who knows anything at all about this stuff-----which is pretty much everybody here).
Bottom Line: Not much finish equals not much value--never mind the serial number. You'll almost certainly find the serial number other than on the butt of the gun, but back to bad news again, the only serial number that counts is the one you don't have---as far as the law is concerned----and you know how those law folks are----picky, picky, picky!!
Ralph Tremaine
And no matter how careful the folks who removed the number were, the folks who made the gun were more careful. So, we've looked on the butt, and we've looked on the cylinder. Let's turn our attention to the barrel. Open the gun, and hold it by the barrel. Raise the barrel latch. Look at the rear of the barrel on the right hand side (rear of the barrel--inside the recess where the latch lives). Good light helps---and a little magnification doesn't hurt. Got it? Great! And if you don't got it, clean out the recess and look again. After you're absolutely sure it's not there, I'll still bet it is, but I'll have a look at the back side of the ejector.