So after talking on the phone with Dave (Spare) I went out and pulled of my seat and pedestal.
Guess what, no big center hole ( YEA ) and six stainless 3/8 oval heads wood screws going right through the about 1" Thick wood floor.
You could just not install it,sell it to me!!!! Lol!!!! Sweet leaning post by the way. Good luck on the install.