Below is a re-post of how I've answered this question in the past.
Let me make a couple of general suggestions.
Make the inwale splices long enough to go a good ways along the deck, at least far enough so that you can get one screw in on the splice into the deck.
I strongly suggest using Titebond II as your glue. I prefer it to epoxy because TII has a very fast tack, whereas an epoxy glued joint tends to slide around a lot: you have to take a lot of care to get an epoxy joint to stay in place. (I did a post on TII versus epoxy once and got a good debate on it. It’s never failed me in water exposure situations. I know a guitar builder and boat builder who swears by it.)
Cut the end of inwale that extends past the deck just a little too long. When you’ve both inwales fit and glued, you’ll have to cut and fit the ends so they butt neatly. More about this later. (An option here is not to glue the splices in place right away, but rather secure them in place with 2 screws, one through the splice and old inwale and deck, one through the splice and deck: that way, you’re not committed and you can take out the splices to work on them. Or discard them if you really screw up. Then glue them in when everything fits right.)
A big problem is to fit the top of the stem into something. Building from scratch there are a variety of methods of securing the top of the stem. However it’s almost impossible to adopt these to inwale splices.
What I did at this stage was to add some wood to the area by building a false tip. I cut a small piece of wood (of ash or any hardwood would do) as wide as the deck plus both inwales so that it could be screwed in place under the inwales and deck, out of sight. Into it I mortised a one inch by ¾ inch by six inch wood shaft, aligned and dimensioned so that it could serve as a backing for the stem and the stem splice. When your stem/splice is finished, it is screwed in place to the false tip shaft from inside the canoe: you don’t have to mess with fitting the stem into a mortise in the inwales.
The advantages of the false tip approach to this common restoration problem are obvious. It’s relatively simple to do and your cutting and fitting of parts can be done on the workbench rather than on components in situ on the canoe. It also adds a great deal of structural strength to the tip: it essentially re-enforces the whole area. Of course, if the tip of the model of canoe you’re restoring is very sharply curved, it won’t be as simple as fitting relatively flat parts together.
Bill Conrad also actually uses this false tip method too.
As for cutting the ends of the inwales that extend past the deck, this ain’t easy. You need a very sharp backsaw and go slow. If you use the “screw first, glue later procedure”, you can do this so that everything fits just right before you glue. Just nibble away at the ends and use a thumb plane and sandpaper as the fit gets better.
You can make the inwale ends flush with the stem, so you can bend the stemband over the deck, if you like that look. I don’t like that look so I let the inwales extend past the profile of the stem. When I put on the stemband I don’t bend it back over the deck but anchor one end under the (extended) tips of the inwales.
