Ebay 10 round M1 Carby mags

[JimF4M1s (Deceased)]

Magazines look genuine, not knock offs. I can't tell about the material used on the pouch from your picture.

C-S'G' (C with an upside down T in it) is a Saginaw S'G' magazibe made by J.L. Clark Mfg. Co. with a type 3 base.
IO B is an I.B.M. magazine. Made by Owens Illinois Can Company, with a type 5 base.

The pouch is a type II with belt loops on the back. There are WW2 dated type II pouches. Type I pouches came out first. Some call them stock pouches, but they were made to snap onto a belt. A enterprizing person noticed the full sleeve would slide over the stock. The only examples I have seen made by Ranier Bell were marked as yours, 57.

Here are some WW2 dated type II's in my collection of over 300. Most marked inside the flap, but some on the back, 1945 dated.

Type I pouches were marked on the back. Or at least I haven't seen one marked under the flap.