Floor racks are pretty easy to make - a few strips of spruce and some cross pieces to fit between the ribs.
The seats sound like they are original. The back story, according to Benson Gray is that the workers at Old Town used to hand weave the seats at home, being paid on a per seat basis. When the Fair Labor Standards Act came into effect in 1938, "piece work" was outlawed and Old Town started using the grooved seats for the pre-woven cane.
Since seats break frequently, you will sometime see an older canoe with replacement seats that had the groove for the pre-woven cane.