Eddie,
1st.... I seen you posting these same questions on the US Militaria Forum.
We don't take kindly to being played like a 2nd Fiddle

Don't trust us ? Among these members here are some of the most knowledgeable collectors in the World. But many aren't as 'Friendly' as I am
The front area of your barrel that would have the INLAND marking has been cut off...... So no mystery there.
The marking you found under the rear of the barrel on the flat area tells us it's a INLAND barrel, as only INLAND applied those markings. As we said those markings are thought to be INLANDS way of marking Inspectors, maybe shift and working stations.
You also found the markings on the Gas Cylinder that show it's Inland.
Your Magcatch marked on the front tooth EI means that part was made for Inland.
Your Bolt should have a marking on the Right or Left lug. This marking would tell us who the maker was.
Is there any marking on the back of your 30Rd Magazine ?
When you have the Op Slide off, you can just rotate and pull the Bolt out. You don't have to tear the Trigger housing apart.
Or you can pull the Op slide rear tab out from the receiver and just pull the Bolt out to look.
I wouldn't do this all the time just incase it adds any wear, but here is Video link from fellow member
Norwich93CMP that shows you how to do this.
Watch his many helpful videos on 'How To' for the
M1
Carbine.
[video]https://www.youtube.com/watch?v=5i75lpSZgtQ[/url]
Here is a Very Good Book seller and a Great book you can start with:
Shooting Gallery Books -- U.S. M1 Carbines - Wartime Production (8th Ed.)
Anima a mi amigo,
Carlos-Pintor 777