I don't believe that the thumb cutout is for a mauser. It looks like it's made to clear the Springfield.
I see a Mauser stock hacked down to receive Springfield metal.

The tang looks a little high on the left side but OK on the right side.
I see the right side as bad as the left, and a little "dremel" action to make room for the Lyman.

I think someone might have a good candidate for a restoration.
Possibly. Certainly more work than I'd be interested in.
And the restoration would be to a Mauser rather than a Springfield.