With the markings not covered it might be right, but I just did a search of Routledge 121's and looked at several pictures of examples without a rib that also have the markings down on the side where a rib would not cover them, but they also have a stamp with REMINGTON and patent information the would probably be completely covered by a rib - is that moved too? Is the rib raised slightly so you can see if there appears to be some stamping that is covered?

Here's a link to one without a rib that shows all the barrel markings so you know where to look - remington-fieldmaster-model-121

In the picture showing the rear of the rib it looks like there might be a light scratch ion the metal running right up to rib just about at the end, I would look at that close to see if it appears to go under the rib. I can't even be sure it's a scratch just from the picture. it might just be a piece of lint.

I do not have a clue to the reason for the small marks in the top of the ejection port, they might have been for some type of deflector.

Gene