Dura Ace 7400 crank
 

I picked up a used Dura Ace crank (the engraving on the inside of the arm says FC-7400 175 LE) and I was wondering how many speeds this crank is meant to accommodate. I know that when they first started making these units, they were meant for 6, then 7, then 8spds, and then at some point they became labeled as 7402. The chainrings appear to be original and the engravings say: Shimano 53 LF/Shimano 42 LF. What is the best # of speeds to use with this crank, and can it be used with other configurations? Is there a measurement that distinguishes between the different versions of the 7400 crank? ...or is there no difference at all? Thanks!