Would I be right in thinking that the barrel would not need to be set back more than one turn to get good headspace? If so, it would not be difficult to inlet for the new punkin position. Then, I would glass bed the punkin area for a nice fit. The Model 70 Winchester, after all, had a screw into the punkin. This would be a nice, small way to get into stock work and glass bedding, and your fusil would remain largely original.
But, if the headspace problem is caused by locking lug mortices set back, ALL THIS IS MOOT.