rembo,
The Centurion is only slightly different from most commercial Mauser actions. It is a commercial receiver that was manufactured in Spain. Look at the left side of the tang and the word 'Spain' should be stamped there. The strange thing that you mention is the military style bottom metal. de Haas states that the bottom metal should be alloy and have the look of commercial floor plates. The latch for the floor plate is supposed to be inside the trigger bow.
There were two models: the 100 which is an ADL style without a floor plate and the 123 which had complete alloy bottom metal.
The Centurion -- Golden State Arms Corp. is located on the magazine and the barrel is roll stamped "Pasadena Arms Corp." along with the caliber designation.
The trigger is a single stage military style instead of 2-stage.
The serial number should be on lower left side of the front ring and have a letter as a prefix.
More detail can be had in the de Haas book.
Regards.
