I've got a pristine 1903 Springfield, so I'm familiar with getting my thumb out of the way. A couple of smacks on the nose is a good teacher!
I'm looking at a photo of Simon Ward who played "Young Winston" in the movie. He is holding the C/96 Mauser left-handed, hammer cocked. He had suffered a sabre injury, hence the 'weak handed' mode. The safety has been applied and the bolt would appear to be well above the web of his hand.
Also in a back issue of Guns & Ammo 'Surplus Firearms' magazine, Dennis Adler is shown shooting his C/96 with and without shoulder stock. He appears to have large hands and yet with the hammer cocked, it does not look like he is in danger of the web of his hand being hit by it, much less the bolt.
He does, however, mention that recoil batters the web of the hand against the square edges of the frame, commenting "If any gun needed a better grip design, this was it!" I can't see how aligning one's thumb on the right side of the frame will alleviate this battering.
So, I'm wondering what you guys know about holding/shooting the C/96 Mauser that I don't know. I have a pal with a "Red Nine' C/96 c/w shoulder stock. I'll give him a call later this evening and get his opinion.