I did grind the edge about 4 inches past the edge of the plywood. I did not do under the plywood. When checking with a fiberglass shop they said no need to grind under the wood.
I was planning on grinding it all down so I could epoxy the board to the fiberglass. I am not thrilled with the thought of doing this so I am collecting other ideas. I see you avoided this by riveting the board down.