It'd be tricky to get them looking properly Eldar-y. I've tried with a couple of my early attempts at Exodite Guardians.
You've got two options really. The first is to try and attach GG capes to Guardian torsos, and then onto the GG legs. This is probably the trickiest way, but would look the best
IMO.
The other way to make something that would look good would be GG legs, bodies, torsos and capes. Then Guardian helmets (would need a little modification to the neck stub) and then Dark Eldar Dark Lances for the Ranger Longrifles.
Maybe cut the arrows off the cloaks too as they'd look out of place and replace them with some of those Guardian backpack vane thingies.
Should look alright