My 458 Lott, my current 416 Rigby and my 2nd 416 Rigby about to be rebored and rethroated to convert to 450 Rigby - all RSMs, with the only stock modification made the replacement of the Ruger factory recoil pad with a LimbSaver pad - provide the recoil control I need to handle those rounds.
I won't disagree with your theoretical list of characteristics to design your ideal stock for a heavy recoil rifle, but IME with the Ruger RSM, the factory stock works just fine. Of course, I've invested a lot of time, ammo and painful lessons with other heavy-medium and heavy caliber rifles, in learning how to shoot them.
Modern classic factory stocks in quality DGRs I have personally shot, in most cases, have not been the LIMFAC. IME proper shooter technique has been the determining factor in providing enough recoil mitigation to control recoil well enough to allow repetitive fast and accurate follow ups. YMMV
BTW, even though there may not be any off the shelf replacement stocks available for your RSM, with the detailed list you've provided, a suitable blank, and a medium-sized stack of greenbacks, there are a number of excellent stockmakers who could turn out your ideal stock.
