I would plug the hole in the rib with pin held in place by locktight, but solder would work, just not very pretty. For the buttstock I would turn a piece of similar color walnut slightly oversize in a lathe and taper the leading edge as well. The season for turning a dowel as opposed to buying one is you can get the correct grain flow to best match. Use white glue as it is the least visible.

www.bertramandco.com ACGG professional, imports, sales
[Linked Image from i.imgur.com]