The markings on the barrel flat make it Inland, Gas Cylinder I-I is Inland made and I believe thru the carbon I can see 2 letters on the end of your gas piston, so that would be a Sub made part for Inland. The rest of the barrel shows no milling grooves. So likely polished away with the Inland name and date. Then the obvious refinish like many were in the 60's to look 'Pimpy'.
You catch what we mean by the late serial number right? Made to go fast when you wanted it to.
ETA: Is it registered as a M1Carbine?