Whether the 7400 FD will work depends on the chain (8s, 9s, 10s) you use, and that depends on how many speeds the drivetrain will be. For 8s and above, the FD should correspond with the number of shifts. You can get by with a 9s FD on a 10s system, but a 7/8s FD may drop the chain easily. As for the 7400 rear derailleur, I seem to recall it having a different cable pull ratio (Dura Ace only) and therefore will only index with the 7 or 8 speed system.

Congratulations on the 7700 find. Those are some great looking and performing parts.