I think you have touched on couple of things that may be causing your recoil problem and the blood marking the rifle is giving you.
One for sure is the size and cut of the stock.
Even though you are shooting a 12 pound rifle the stock is thin and not making a large foot print, so the recoil is being received in smaller condensed area instead of being dispersed over a wider area of your shoulder.
I was going to recommend a lead sled shooting rest to you if you can use it with out skinning up that beautiful rifle.
I have a friend that uses one when shooting his Remington Ultra Mag from a bench, he swears by how great it is.
The other thing is the shooting position you described, (hunched over the gun).
I kind of think that maybe if you were in a little more straight up sitting position your body would not be as rigid thus letting you move more with the recoil, that may help some.
That being said at one time I collected old double barrel shotguns, had one in my collection that was a 16 gauge; that gun kicked like the proverbial mule.
I shot one shell through each barrel, besides it hurting like heck my shoulder was blood marked like I had shot several boxes of shells, never shot that gun again.
I talked with an old gunsmith about it, he thought the stock was cut wrong.
However as beautiful as the wood is in your rifle I would consider other alternatives before I would cut that stock.
As others have suggested, different (lighter) loads may be your best choice.