Is secondary extruder wire harness same for Dual & FlexyDually?

Is the secondary extruder wire harness the same for the Dual Extruder V2 and FlexyDually V2 tool head?

If so, can the tool head without all the duplicate items be purchased (In order to save some money) assuming you already had one of them?

Yes. The only possible difference would be that the newer ones may or may not have the ground wire necessary for auto leveling, which could be added. You can see what plugs in where here:

The secondary extruder harness does not need the sense wire, as the primary extruder has the auto level on it.