You do understand that the M1 Garand and the M1A operate on two different action types. The Garand utilizes a long stroke gas piston system, where the M1A uses a short stroke system. The feel of shooting each rifle is a bit different due to this fundamental difference. While they look somewhat alike on the outside, they are not the same on the inside.
The CMP has excellent service. If there is an issue when you get it, they will either take it back and fix it or send you a replacement part.
Perhaps a word about the M1 Garand would be helpful.
As a kid in Chicago, I marveled at the "Checker" cabs that ran all over the city. They were big, boxy cars, ugly as sin and built to be rebuilt. If a Checker cab blew an engine, a new one was swapped and away it went again! Bashed in doors, seats, front ends, trunks, all of it was designed to be swapped out as the need would arise. No Checker cab ended up with the same parts that it started out with.
M1 Garand rifles were handled the same way. Even in the original assembly factories, the Winchester line may have installed Springfield barrels. Springfield may have run short of trigger housings, so International (IH) parts were installed. There was never any intention of making an ALL Springfield, Winchester, IH, H&R or any other brand of M1 rifle. Your best odds of getting all the same brand of parts on any particular rifle are with Springfield as they made the largest number of rifles.
As the rifles were returned for repair, defective parts were replaced with any of the manufactured parts. The parts went where the need was greatest. There was NO effort to keep the entire rifle brand specific.
The wood stocks were done the same way. They were sanded each time they came in for repair. I had a 1903A3 that was sanded so many times that the wood is reduced in size all the way to the stock reinforcing bolts. That is 1/8" to 3/16" reduction in size all over! So....when I hear someone griping about new, (and larger) stocks available for the M1, and comparing them to the sleek, smaller "sanded to Hell" examples they became used to seeing, I gotta laugh!
If you see an M1 that is made of all one brand of parts, knowing what we know about how these rifles were manufactured, you might suspect some fiddling with the parts on the rifle to make it more "collectable".
The rifles made by Winchester, IH, H&R are considered more collectable and valued higher. The real truth is that Springfield made the largest number of M1 Garand rifles and they also kept up better on the repeated changes to the rifle as production went on. The smaller manufacturers lagged behind in implementing those changes. That's one reason why I prefer the Springfield rifles.
As the war raged on, they began having trouble with the M1 receivers under the load of grenade launching. They took the Garand receivers and dunked the rear of the receiver in molten tin to draw back the hardness of the receiver at the rear. This accounts for a slight difference in shade/color of receivers in the rear inch or two.
The M1 Garand receiver is a marvel of metallurgy and machining. To duplicate that receiver in today's Dollars would make the rifle horrendously expensive. Companies like the new Springfield Armory (No relation to the old Springfield) must use precision castings to simplify the receiver processing. Once surplus receivers dried up, castings replaced them. The castings are fine, safe and precise. They are made with new technology instead of the old technology. They just aren't the same as the old receivers.
Don't know how anal you want to get with your rifle, but here is a data sheet that many fill out to document the parts inside. (Yeah, I have one or two of these filled out somewhere )
A lot of guys want their Garand to have the exact same type of parts as it should have left the factory floor with, and use stuff like this to find out what 'should' (but not necessary the case as explained by Flash) have been installed at the exact time of manufacture. There is a pretty big trade market for parts as owners try to swap this and that so that their gun is 'correct' to them. None of which mattered in the field as the armorers job was to provide the soldiers a reliable and reasonably accurate gun that went bang every time. The only people who cared that a H&R branded rifle had a Springfield trigger group and a Winchester operating rod were the guys that came after it's fighting days were over.