Thanks. Unfortunately, the canoe is 104 years old and the existing planking is severely dried out and far too brittle to provide any structural integrity. Complicating the replacement process is the existing planking is 4-1/8" wide and the only new planking that I was able to procure regionally was 3" wide. So nothing will match width-wise. I'll struggle through it. Just though there might be some best practices or tips out there on how to tackle the complicated amidships area.
Hmm...boy howdie. Here comes the peanut gallery with a few observations.
First, I would not consider 104 years to be unfortunate....not one bit. That it's over a hundred years old is a blessing and something to preserve....
Most of my boats are about that age or older and I have kept all of the original planking in place except where it's broken or very warped. I do as 1905 Gerrish notes and apply a "boat soup" to the planking after I have finished the repairs. I blend linseed oil, turpentine and mineral spirits and heat it before applying it.
I would not consider completely re-planking a boat......if the planking is so bad that it warrants that I wouldn't own it. That said, I have never seen one that was that far gone.
Given that you started re-planking with smaller boards you've kind of put yourself into a bit of a bind as far a finishing goes. Now your questions about the gore and how to get around the tumble home start to make more sense...What you are trying to do will not be easy unless you do it the way 1905 suggests, one board at a time. Keep in mind that the planking was originally fit to the hull on a form.....
So...given that you have already re-planked the bottom and given that the rest of the planking is probably fine.. what I might recommend as a next step is to stop and figure out how to make a transition from the 3 inch planking to the original planking. Then see if you can source the wood you need to patch in any pieces that are in need of replacement while keeping the rest of the hull as original as practical/possible. The other option is to tear the new planking off.
Keep in mind that you probably have a red cedar hull. I have made wide red cedar boards by sawing red cedar siding... There are probably other ways to get the wood you need. I always save pieces that I remove and am often able to refit them to other spots. The nice thing about used wood is that it blends..
Pictures would be helpful......it's hard to envision your process...