Cut, chisel, cut, glue. Easy as that really.
*UPDATE*
Turns out I didn’t get a shot of the repair specifically beyond this stage. I went through other photos to find one later.
You can see how it faired out in this shot below. I’m fooling around with getting the decks shaped, but the gunwhale repair is there too. This was the first round of maple decks that I ended up scrapping.