From a custom gunmaker's point of view, do what you want with the action, but trying to make it into something that it is not, would lead to failure of sorts. Trying to mount a tang sight, eliminating the tang safety and ejector along with a target type stock would destroy the virtues without enhancing the results, IMO.
Look at it now, ruined as a British Falling Block sporting rifle, what it was designed and built to be. It could be a very fine contemporary custom sporting rifle, not restored, not appreciably altered, just renewed for a contemporary sportsman.
As said in an early post, it is yours, do what you want, but as a gunsmith I wouldn't want my name associated with what you have in mind, which amount to ruining a singular piece. But neither do I believe "the customer is always right".
Steve (SKB) or Glenn could build you a very fine sporting rifle from the action, but I wouldn't ask them to make hash out of it. My opinion.
