If you are purchasing a new SA M1A, it will not be a USGI bolt. SA stopped using them in their rifles years ago.
Current Springfield Armory bolts are marked as such:
7790186-SA
F00072
If you want a USGI bolt, you're going to have to get yourself a good set of headspace gauges (I'd recommend the Clymer gauges) and start buying bolts until you find one that fits. Barring that, you could find an unissued bolt and lap it into the receiver, or have a gunsmith do it for you. It won't be cheap though as the lapping can take hours and labor costs can really add up.
I got lucky when buying bolts. Bought 2 lightly used TRW bolts to try, and both headspaced correctly in my SA M1A "Loaded". The better of the 2 is now in the rifle, with the other kept as a spare. I use the SA bolt as a paperweight.
Overall, you should be fairly safe with the SA bolt. The current batch are considerably better than the problem bolts that SA issued back in the mid 80's. The 80s bolts had no markings whatsoever, and were failing quite a bit, prompting a recall from SA. I have only heard of 1 current production bolt actually cracking the locking lug. The only other deficiency that I've heard of with SA bolts is that they seem to slip the extractors on a regular basis. That's an easy one to identify. Remove the bolt from the rifle and check to see if the leg of the bolt protrudes through the bottom of the bolt. If it does, you can either file it down flush, call SA for a replacement, or replace it yourself.
There's very good info on M1As and M14s over on:
www.battlerifles.com
