you CANNOT remove the folding stock to turn it into an overgrown TC .... it is ILLEGAL to convert a rifle into a pistol .... by removing the folding stock you in effect turn it into a "sawed-off" rifle .... that would get you a quick trip to "Club Fed".
If it is a new weapon (post ban), it doesn't have a bayonet lug, and you CANNOT add one. That would make it a prohibited weapon under the so-called "Assault Weapons" ban .... it would also get you a quick trip to "Club Fed." NOR can you add a folding stock to a "post-ban" weapon. So you definitely want to purchase a "pre-ban" gun if you want those items.
Regarding the polymer stock, my gun guy thinks that they are available (straight stocks, anyway. He's not sure about polymer folders). You might try checking at Cheaper-than-dirt. Hope this info helps you. This is NOT intended as legal advise. Be sure to check the laws of your state VERY CAREFULLY before purchasing any weapon. Your mileage may vary. Not responsible for lost or stolen items. Close cover before striking. Don't drink and drive.
M1 Carbines are fun to shoot and ammo is relatively easy to come by. I wish I hadn't sold mine .... :(
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