I shall be changing the cylinder head on a friend's 300 tdi this weekend. He bought a new head but we shall be swapping valves, injectors, etc over. The valves were very recently re-cut and lapped in and the engine has only run for a couple of hours (the head turned out to be cracked internally, hence filling and skimming was a waste of time and money). Do we need to re-lap the valves when fitting them to the new head?