first , i agree with bubba, and the point of the other members here.
Zonie`s point is also well made, however, looking at his repair i would have assumed that it would have been an arsenal repair, you see many military rifles with similar repairs.
when did my first build, it was from walnut. of course, while i was drilling the ramrod hole the bit came out the belly of the stock. i repaired this by cutting out the entire belly the width of the hole and glued in a piece of walnut with a similar colour. i used titebond III, and finished the stock with linseed oil followed by tru oil.
you can see in the pic the wood difference, and the gap where the glue in was not perfect. this showed up during the final shaping. i might look at filling it one day. what you don't see is a non stainable glue line. titebond III dries brown. the lighter colour is reflection.
https://i.imgur.com/zegdXgE.jpg
now as this is on the belly, i don't see it or even think about it. its not for sale so I'm not worried about having made 400$ worth of parts into $200.( i got a good deal on a "kit" from another CND member of this forum)
i have a fowler build in progress using flame birch and recycled parts. it is laminated from two 5/4 planks perfectly mated and fitted. with proper planning and layout, there will only be two places where you may readily see the grain difference and that will be the short space between the front of the trigger guard and the ramrod entry thimble, and the front of the comb on the butt, but carving will mask some of that.
all other glue lines will be under the barrel and long tang, buttplate with an extended comb piece, under the toe plate, trigger and guard, and ramrod.
a sharp eye will pick out the grain difference on each side of the stock, but i spent some time lining those up to be less noticeable.
once again, not planning on selling it either, not a fan of selling guns
also of note is that the widest part of the stock is under 2 inches, no cheek piece as i shoot from both sides, depending on the situation or mood I'm in. the potential inheritor of this also shoots right or left.
all this aside, most of us here on this forum have or have had at least one stock made from two pieces of ugly wood with a brass spacer.........and lots of members here love to hate those.
and the wood 9 out of 10 times, does not match either
if you plan it and do it right and are doing it because you want to( i think a book matched stock of quilted or curly/figured walnut would be nice), go for it.
on the other side, using one piece of wood is the classic and accepted approach, and as this is a traditional forum....its up to you