Visually wise nothing much, the stock shape is perfect and iconic, the only two things I'd do is keep the skip line checkering but get rid of the scrolly bits and make a left handed stock, so the lefties can enjoy it's magnificents, internally just revert back to the early short stroke pistons (like mine) and use a synthetic top hat, other than that it's perfect apart from the weight and if they could lose a pound or two in that area then even better.
And I would not have chosen the above geeky looking Airsporter "centenary" model to go by, the standard Stutzen barrel length is far better looking.
Pete