I don't know what wood was used for the blocks on which the toggles were mounted, but I would guess that they were made from scrap rib stock. Here are a few pictures from 5 different Morris canoes -- some boats seem original, others restored. The blocks appear to have been fastened with two screws in diagonally opposed corners of the block.
It's a very simple system. The brass is a section of stemband with a hole drilled in the center. A brass escutcheon pin runs through the brass and through the wooden block, then bent over underneath the block. There are 4 of these blocks (in a 16-18' canoe), each screwed down to a rib, each block being about the thickness of the floor rack slats. Place the floor rack in with brasses turned parallel to the long axis of the canoe, turn each brass 90 degrees, and the floor rack is held in by tension.