Need help identifying this gun

[Gene Oliva]

Hey guys, usual story. I'm a gun guy, but not a shotgun or old gun guy. This is a family gun and the owner seems to think it's very valuable. I'm not sure if it's a valuable as he thinks.

I know nothing about this shotgun, so I appreciate anything you can tell me. I've blurred out the last 3 digits of the serial number.

What model? What gauge? How old is it?

Is it ok to clean the rust? I know for coins you should never clean them. I don't want to find out that by cleaning it I ruined the value for him.

Thanks,
Gene