Anything that doesn't feel good to your paw needs to go. Balsa side chunks would make it easier, but the pine (?) isn't too bad if you attack it with the correct tools...coarse wood rasp, very coarse sandpaper, etc. There's way more wood there than you need, except perhaps where some may need to be added (per Mr. Buck's instructions) to make the handle fit snugly on the index and pinky fingers.
I hope Brett wasn't making fun of the thumb locator on my Chris/Alan/Arkady CF handle, 'cause it's peachy. Helps keep my thumb from drifting upwards. All the other fingers are a snug fit, so why not the thumb?
Steve