To my knowledge you will either need a waterblock custom made to fit the mounts on your motherboard or wait for waterblock manufacturers to pick up on the board's popularity to manufacture one for the masses. In short I'm not aware of a waterblock that is available to drop onto the Z170A-G43 PLUS.
Or will what's sticking up out the board restrict watercooling MOSFETs on this board?
It hasn't been made by XSPC, EK, Bitspower or the likes e.g: diamond cooling. You could contact Diamond Cooling and see if tehy can manufacture a waterblock for you but they may require your board to take measurements and weigh up the intricate mosfet heights and locations on the board to avoid and clearance issues and also provide optimal cooling to them. In essence the request is so that they can make sure the block will go onto your board without an issue.
If you're new to watercooling, you should check out the watercooling sticky(located in my sig) for info.