The LMR barrel is an especially good shooting barrel if it isn't worn out. LMR's were highly sought after for making match rifles as late as the 80's--that's how good they are. It appears that your rifle has correct parts according to its serial number. Don't get into the "matching numbers" game with an M1 rifle. The ONLY serial number on an M1 is the number on the receiver heel, the other numbers are part, or drawing numbers. 6528291 on the side of the receiver leg is the part, or drawing number. The "T" has to do with the material supplier and lot number. The barrel is dated January of '55. Judging by the rifle's s/n I'd wager that the barrel and receiver are original to each other. H&R used barrels of their own manufacture and LMR barrels if their barrel production slowed down. About 25% of the HRA rifles have LMR barrels. It is not a rare combination. The barrel markings are thusly: LMR (Line Material Co), the barrel maker. D65.....the part number. 1 55, date of barrel manufacture, NOT necessarily when the barrel and receiver were mated together. A40 is the barrel heat lot number. The proof "punch" mark. "M" means the barrel was magnafluxed to check for imperfections. Finally, the DoD (Department of Defense) acceptance stamp. If the mark above the DoD stamp is a "T" it means the rifle was targeted.
The dimples on the ends of the hammer pin are an HRA trait as are the dimples on the ends of the locking lugs on the trigger guard (some IHC's also have the afore mentioned dimples. They are unique to HRA and IHC). The bullet guide appears to be correct also with the little half-moon cut out on the side. That has significance in that those with the cut out have a higher lobe on them for engaging the op rod catch. A picture of the staking of the lobe will help to identify possible originality of that part.
The *U* on the bolt shows that it was made for HRA by Underwood (the type writer guys).
Unfortunately I can't zero-in on the important aspects of the stock to give you an honest opinion of it, but it matches appearance wise, to the rest of the finish over all. I don't think it is a replacement stock, just well-used and possibly heavily sanded. Are there any stampings on it?
Over all, it appears you have a nice, well-used, representative example of a mid-late production HRA M1 rifle. Shoot it, have fun with it, and be proud of it.
Hope this answers some of your questions.
Jon