With weight and strength both an issue, you might consider replacing only two of the eight bilge keels -- to provide fore/aft strength and stiffness with minimal weight gain. The price to be paid, of course, is some limitation on quick maneuverability, but that might be a worthwhile trade-off. The split branch ribs of your canoe are very unusual, and if it were my boat and I were replacing or adding ribs or half-ribs, I would try to match them. But with weight and issue, I might opt for leaving the ribs as they are -- they have apparently been sufficient until now, and will probably be sufficient for the future, unless you are contemplating using this canoe in heavy white water. If you look at the construction of old Trailcraft kit canoes, you will see that they were quite lightly built (except that they did have a fairly sturdy interior keel or keelson), and that your canoe's structure compares favorably. See the first two attached pictures. However, what I would probably do is not replace the bilge keels, and not add any ribs or half-ribs. I might replace the main keel, for the strength that it would add, with minimal weight But I would build a set of floor boards, which would both protect the bottom of the canoe, and spread the weight of any load on the bottom (feet, beer cooler, knapsack and tent?) widely over the ribs and planks. For carrying the canoe, the floorboards can be removed and carried separately. I would build them lighter, as in the attached picture of floorboards from a Morris canoe needing restoration, rather than heavier, as in the attached picture of overly-sturdy floorboards in a home-built or kit canoe. I will leave the issue of what wood to use to others, and if you poke around the forums, you will find widely varying opinions on using linseed oil on planking. If the outside surface of your planking is quite fair and smooth when restored, you might consider covering with dacron, rather than canvas, to save several pounds. Again, if you poke around the forums, you will find information on the topic -- use the search function. Keep us advised, with pictures. You have a neat canoe.