cas sensor

Hello, I am changing my water pump and need to take my CAS off. I know I've got to mark it etc but then when I turn the crank with it off to line up tdc will this not make the CAS off when I re install it as the cams will be in a different position to when I took it off so how do I make sure...

Can anyone help me find a CAS sensor for my R32 Gts-t. Went to Nissan and they said €790 for it. Any links would be helpfull. New or second hand as long as it's in perfect working order. Thanks.