Its hard to say without PHOTOS

but the stock may be more of a problem than the bore cost wise. The first thing I would do is to measure how worn the bore is. This could be done crudely by seeing how far down the barrel a .311 or .312 bullet free falls down the barrel. If it falls only part way down the bore, then the cheapest option to try would be to lap the barrel and see if .323 bullets shoot any better ( assume from your description that the barrel has gone past trying .318s). There's a good description of this in the Spring 2008 Double Gun Journal. I may be wrong, but my gut tells me that reboring to .366 of .375 may be pushing it too far. You could also look into some of the flanged .358 cartridges if it really needs a rebore.... If the first step works with the .323 bullets, but you want more speed, you could think about improving the case along the lines of the .303 Epps design... As for stocks, you need to discuss this locally, but if you were in the UK, you'd have to be prepared to stick your hand in your wallet to the tune of at least Ł1000, more if you want better wood and finish.