Parts needed:
D2S bulbs, ballasts, relay harness
Maxima (Black Series from TRS) projectors
Factory legacy h7 halogen projectors
Black Series clear projector lenses

This guide begins after you have already opened up your headlights and removed the projectors. Plenty of good guides out there for that, this guide will specifically cover building a bolt-in OEM D2S projector. There is a Retroquik kit available for 4th gens, but that uses a MH1 projector with H1 HID bulbs. This will allow you to run OEM or aftermarket D2S HID components.

Here we have a Maxima D2S projector (left) and the stock Legacy projector (right). Look pretty similar, don't they? Mounting points on the shield are a bit different between the two, but we'll get to that in a moment.

The projector is held together by three screws, with the reflector bowl and lens holder sandwiching in the cutoff shield. Remove those screws on both projectors to split them into their individual parts.

To swap in your clear lenses, slide them into the lens holder backwards to disengage the clips from the stock lens, then bump the stock lens with your palm to knock both lenses out of the holder. Insert the clear lens until it locks into the clips on the holder. Both projectors use the same lens holder, so it doesn't matter which you go with. Here we have the parts used for the hyrbid projector: the maxima bowl, legacy shield, legacy or maxima lens holder with clear lens installed.

You will need to cut/file down three nubs on the Maxima reflector bowl.

Now you can assemble your components and put the screws in. You now have an OEM D2S HID projector that bolts right into your Legacy headlight. Maxima projectors respond well to tuning, so play around with the lens spacing by inserting thin washers between the shield and lens holder until you get a level of sharpness and color band that you're happy with. Mine were good to go as is.