A rack grade M1 garand is not going to be as accurate as a K31.
There are lots of people who claim to own 1 MOA rack grade Garands, but I am not one of these. Below are targets fired with various rack grade garands, some with ball, some with good ammo. The 19 shot group is with good ammo. All targets are at 100 yards.
It is a good rack grade Garand that will shoot within 3 MOA. The criteria for a 1950's new NM Garand was 3.5 MOA with NM ammo.
The lower target is the old 5V target, used at the National Matches up till the 60's. I don't remember when the decimal target replaced the 5V. However, look at how large is the highest scoring ring. All you have to do is hit the black, and you get a 5. That was the capability of the rifles back then.
Incidentally the group I have on that target was fired in a club 200 yard Garand Match. We had a match rifle category and that group is what I fired with a match grade Garand prone.
A match grade Garand will shoot as well, and maybe better, than a K31.
The Garand is a much better battle rifle than a K31. As for reliability, don't know. The Garand was developed into a highly reliable rifle and I have shot tens of thousands of rounds through them. I have shot less than 500 rounds through a K31 and no one I know shoots them in competition. I suspect the K31 has some weak spots, but you have to figure that the Swiss got most of the bugs out of the system in 30 years of service.
200 Yard Old 5V target