Well as you can see in this picture I made hand carved wood filler blocks and epoxied them in place. Then I refinished the stock. You can see where I did it but you cannot feel it. It's been that way for decades now.
I was going to add all the select fire parts on one of mine but didn't like the switch sticking out. I just used to round knob to fill the hole.
I have a usgi glass stock for mine. I've always intended to fill the hole with epoxy and paint the whole stock in olive green and sand. One of these days.