Looks original to me. I had a couple of original SA/GAW stocks that showed the original sanding pattern running about 30 degrees to horizontal like yours.
Here is another photo of the SA SHM cartoucheAttachment 29981
Looks good to me. SHM is not one the humpers fake much, although they do exist.
Here's one I just picked up.
Whoa! Nicest stamped stock I've seen in a while,whatever the stamp.
If I should die before I wake...great,a little more sleep.