Need some help on IBM carbine, please

[Prez1981]

Received an IBM M1 carbine and need some opinions. I'm a bit suspicious of the receiver finish, rear sight, and barrel band. I have posted some pictures below.

On the receiver:
The receiver has a much gray-er finish than I have seen before on M1 carbines. It is a different color than the barrel, as shown in the picture (the exposed part of the barrel may have taken a bath in cold blue at some point in the past - need to do a thorough cleaning to be sure). The barrel is IBM and undated and the witness marks on the barrel and receiver align perfectly. Does this receiver appear to have been re-parkerized? What is going on here? The only thing that makes me think it wasn't re-parked is the perfect alignment of the witness marks

On the rear sight:
The rear sight is marked "S" on the left side only. No markings on the right side or the sight leaf. There appear to be two stakes at the front of the sight and then deeper stakes at the front and back on the side. Two questions: Is the rear sight original or reproduction? Is the sight original or did the carbine have an adjustable sight that someone replaced in the past?

On the barrel band:
Barrel band is a Type 2 with wide swivel and is completely unmarked. It almost appears too new. How can I tell if this is an original part or a reproduction? It almost appears to have a blued finish in the photo, but I'll have to pull it back out of the safe to make sure.

The carbine is SN 3881090. The rest of the parts breakdown is as follows:
BBL - IBM - no date - excellent bore
Rear sight - S on left side, no markings on right side, no markings on sight leaf
Extractor - W-B
Firing Pin - OBB (2nd type in the white)
Bolt - AOB round bolt
Recoil plate - PR-B
Operating Rod - Type A Variation 3 marked AOB and BB (Ruth says that Variation 3 should only have a single letter and Variation 4 should have double letter?)
Trigger guard - PR-B
Hammer - WMB
Trigger - TB
Magazine Catch - PR-B
Safety - EPB
Front sight - SI B
Sear - SG-B (no hole)
Stock - looks to be sanded, but can make out C and B in the sling slot - high cut, oval sling slot
Handguard - SCB

Any help or opinions would be greatly appreciated. I took a gamble and I'm suspicious that it didn't pay off. If this is a re-parked carbine with replacement or reproduction parts, I want to be sure to list it as such for the next buyer when I move it out of the door.

[Prez1981]

More pictures

[Prez1981]

Last picture

[Tuna]

The receiver has been refinished. The rear sight is a repo. If you look at the dove tail you can see where the original flip sight was replaced by an adjustable sight that was staked into the dove tail. That was removed and the repo installed. The firing pin should be a type 3. The slide should be a type 4. Look for an S in front of the C-B on the stock and it should be a birch high wood stock. Your carbine was made about February 1944.