your bolt look pristine compared to mine when I removed that board.
Anyway, like phattyduck said, I had to pull them appart, remove the old bolts then if I remember well.
Then for years they held with a blob of urethane under the board, then last time I removed them, I drilled holes on the sides and now they're held with stainless steel bolts for ease of removal

https://ibb.co/JrfzRyY