I have a Phantom. I do not know if my dagger board is an actual Phantom dagger board, but it measures 41 inches on one side and 42 3/4 inches on the other side. This info may help you determine how comparable the Sunfish daggerboard is to the Phantom dagger board.
Also, I found a web site that advertises the sale of a Phantom handbook and hand made Phantom dagger boards. I have tried multiple times to contact them to get a handbook but have never gotten a response from them. This link is probably useless, but you can try. Maybe you would get a respone with interest in a dagger board.