Sometimes aftermarket M-1 Rifle receivers are okay, sometimes they are not. If you build a rifle out of a non-military receiver and you ever want to sell it, no matter how good it is (or isn't) you will have a much harder time selling it and you will not get as much money for it.
I am a lover of the M-1. If building one, I would only use a receiver made by Springfield Armory (govt. armory, not the commercial one), Winchester, International Harvester, Harrington & Richardson, Breda, or Beretta.
Others will tell you theirs built on CAI, Lithgow, etc. is okay, and I am sure that they are. But you do not hear people with rifles built on the above listed receivers complaining that the rifles do not work well because of receiver based problems as a general rule.