I have the oportunity to purchase a National Postal Meter M1 Carbine. On the receiver it has US Carbine 30 cal M1, National Postal Meter. It has a 1456XXX serial number, Irco rear sight (from what I can make out of it) and the barrel has Underwood-43. The stock is in excellent condition, has 2 magazines (20 rnd) and has the olive drab snap on sling. Can anyone tell me about what year this may have been produced??? What is it worth???