I’m not a big fan of keels on canoes but they do help the boat track better on lakes where wind can be an issue. On a river a keel can be a real hindrance, impeding maneuvering or worse, hooking a rock and sending you for a swim.
The 50 lb, as most older wooden canoes, was originally fitted with a keel. Every other rib already had a hole along the centerline so I gritted my teeth and punched through the new canvas, filler, and primer.
The 50 lb models were built light with thinner ribs and planking than standard so the keel will add strength and a little protection.