the clocks will need coding to your ECU/keys as the immobiliser needs syncing. This is done through VAG COM. You will also need to extract the SKC from possibly both clusters and the mileage will need adjusting. This is done with VAG TACHO. You'll also need to fit some new wires from the wiper stalk to the cluster multi plug and also a wire from the multi plug to the bumper for the outside temp sensor.
Clocks are easy to pull out and change over, wiring is a bit fiddly and wiper stalk is a PITA as you've got to take the steering wheel and other bits off to get to it. Coding the clocks/keys is a bit tricky first time you do it but easy enough once you know your way round it all