Looks like both 7400 and 7402 cranks should fit perfectly on a 7400 bottom bracket axle.
Here is a Shimano parts and specifications sheet for the Dura-Ace FC-7400, FC-7402, and BB-7400 which I just uploaded. Parts descriptions at the bottom of the page also show possible interchangeability of individual parts with other Shimano models of the period. This was printed in 1989.
http://farm5.static.flickr.com/4128/...bdfc60e9_o.jpg