chaosrob,
Welcome to the Carbine forum. We have an experienced and knowledgeable group here who will comment on just about anything carbine related. Besides asking questions you can use the search feature in the upper right of the page. Finding past threads or posts on different topics that might be interesting reading.
You already know your Inland has been through a rebuild by the mixed parts and later parts added. I have seen a few with the serial number in that location, but can't remember the particulars of how or why. I have seen some imports stamped there, but they also had other parts stamped as well. The usual place to restamp the serial number when blocked by installing an adj rear sight was in front of the dovetail. My reference books and Carbine Club newsletters are still packed from my move. Maybe someone with access to theirs can assist.
There are some good reference books available. Probably most notable the "War Baby" series by Ruth, and for a quick handbook "US M1Carbines, Wartime Production" by Riesch. If you are not already, you might consider joining the Carbine Club. It's was started in Nov 1976. They put out a newsletter that was originally monthly, now quarterly, with great information about the M1 Carbine. You can also purchase all the past issues dating back to 1976. I just received my latest Jan 2015 which is number 381.
The Carbine Club - A CMP Affiliated Organization
Enjoy the forum and look forward to your participation.
Jim