the weight may not be the issue, the issue is the length....its already a long gun.
the 460 stock may be better, i have looked at modding my 440 stock here but decided to carve a laminate stock instead, the but pad can be moved forward but the distance from the pistol grip to the trigger is too long also so its easier to make a new stock and maybe sell this stock on once done. The sporter stocks have better ergonomics IMO, the 440/470 stock is nice but build for 7ft Germans with hands like shovels..not 5ft 10 brits
I have a stock design now, a mixture of 440/CS800 which I think will work well, im considering making it ambi also so its easier to carve as everything is central and not offset.