Thanks for the info. Both the Carbines I picked up have zero time or low time GI parts in them and apparently the receivers are fine. Neither slide will come loose from the bolt without going to the dismount position.
Interesting information about the M2 slide. I just bought one for a spare but haven't got it yet. Will check its functionality out carefully. I also bought a new production forged flat bolt from SARCO,for a spare. Put it together with new old stock GI bolt parts, and found it headspaces perfectly. Will get the new bolt out to the range in the next couple of days and see how it does. Will be watching it carefully for unusual wear.