Can I use a Dura Ace triple front shifter (ST-7703) on a Dura Ace double front der.? Will the triple shift ok on a double front der. and crankset?

It will shift properly, u will just have to set up the limit screws on the front mech properly. the shifter will still click into three different positions, but the mech will only move between the two chainrings.

Cool! Thanks.