Lance,
Your c-block gun could be correct with a properly serialized Mauser folded metal blue body magazine with the full serial number and SE655 on the base.
But also used in this time frame, i.e. c-block, was the Haenel magazine (sometimes incorrectly called the extruded body) with zig-zag spring, and the Haenel code 122 on the body together with the Eagle 37 acceptance stamp. The Eagle 37 may also occasionally be seen on the concave pinned aluminum base base where the full serial number will be stamped.
So the correct magazine will be serialized to the gun complete with suffix. A period correct magazine will be either of the two types with a serial number as close as possible to that of the gun.
Hope this helps.
John
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