If I swapped to 7 speed (7401) downtube shifters and matching cassette, and kept the 8 speed (7402) rear derailleur, I presume the indexing and travel be correct then, only with just with one less gear obviously? This way it would all be 7400 series; surely the only difference between the 8 speed and the 7 speed 7400 series Dura Ace shifters is the amount of 'clicks'?