Stamp II (also the first element of I) is the highly stylized Germaneagle proof mark.
Stamp I is the German proof mark + date August 1972 + Ulm proof house mark, applied when the imported rifle was tested the law as required for imported firearms.
Stamp III is, of course, in Thai. Can't help you there.
There should be an importer's stamp on the barrel somewhere on the left side.
German proof houses do not apply stamps to the wood, so this must have other origins.
The stamped name on the wood looks like W. GUELDENPENNIG. This is a personal name.
I have seen several of these rifles offered for sale here in Mauserland over the years, the last one a few days ago, and they have always been in dire condition. You have a very fine example of a "smiley cat".