Here is an example of what Targa911S it talking about. This is a picture of the left lock on my great grandfather's shotgun. It is marked W.W. Richards (not THE Westley Richards) and is a Belgian made knockoff of the period.
However, there were back action locks made in the states. The only way to know for certain would be to pull the locks off of the stock and look for proof marks or makers marks. There could be some proofs or marks under the barrels as well. I'm guessing that the barrels come off by driving out a wedge in the forearm. Removing the action screws is something you should not try to do unless you have a set of proper gunsmith screwdrivers to avoid damaging the screws.
Tabs, one reason the barrels are both thick could be to allow for regulating the barrels without having to have an oddly shaped and difficult to make filler piece between the barrels.