My photo is a custom floor plate and your release lever would be different.  The 1909 came with the milled floor plate with a release like you are describing.  Some custom gunsmiths took the standard milled 1909 floor plate and added a button release like I posted to save from buying a full custom floor plate.  The 1900 Argentine Mauser was well made but the heat treatment was suspect and many custom gunsmiths had them reheat-treated.  Most people didn't do the heat treat.  By the time the 1935 Chilean 98 Mausers came along they had better steel and heat treating.  The 1935 Mauser were really well built but didn't have hinged floor plate like the 1909.  I was always impressed with the inletting on the 1935 Chilean.  It was absolutely perfect. 

Frank