I may have to eat my words about the splines being indexed for one position only.... last night I checked a Dura Ace 7700 NOS bottom bracket that I had purchased for a retro road build - and I could not see any difference in the splines, they appeared all the same thickness.

This is odd odd though because I was fairly certain that the 7703 one that I used on my Ultegra 6503 triple crank wanted to be installed only one particular way. I will research this further and report back.