Interesting concept. Got lots of water? Does the spent water get pumped back into the header tank? All sorts of questions come to mind with no solutions to offer.
So, a 12' pendulum, that's some size clock movement.
Interesting project to follow,
Chris of YouTube channel "Clickspring" is well into clocks so may be able to give you pointers to where you may find information.
Good luck with it.
John B