There is no difference between the M1 and M2 receivers except markings. There is no serial number range as the next paragraph shows.
When Inland was making both guns at the same time, they didn't know how many were going to be M1s and how many would be M2's, so they made up the roll stamp with the number blank and stamped it by hand when the gun was assembled.
Now the bad news is that a carbine stamped "M2", regardless of whether it has any selective fire parts, is a machinegun by law, and illegal to own if not registered before 1986.
So first, look around to see if there are registration papers, like a Form 4467, for registration during the 1968 amnesty. If not, you can contact BATFE and see if they have it registered. You might want to do that through an attorney, so if they don't they can't come after you. If the gun is not registered, you have only one legal option and that is to abandon (surrender) the receiver to BATFE or the police.
Some folks might suggest other options, but I will not do that here. Good luck.