The FD is indeed a 70 series Shimano 'cross unit. Very versatile, great for shifting unusual ring combinations. Actually slightly finicky when it comes to trim in this application, so may go back to a nice clamp 7400 FD in the future. Why that FD?
Bercause of the chainring combination- it's a 48/34.
Wait, how do you put a 34 inner ring on a Dura Ace 7400 130 BCD crankset? Why, you start with a 6206 triple crank (same design aesthetic but 110/110/74) and send it over to forum member Stephen Needle in England. He milled it down, polished it up to a mirror finish, and pantographed the Dura Ace logos:
But there's more. Discuss!