"retrofitting" is basically converting a reflector headlight to a projector headlight, that's all.
For your application there are several options you can do:
Bolt in HID Kit:
Basically pick up a pair of H4 conversion headlight assemblies so you can run H4 bulbs instead of sealed beams, I can get these, or you can them elsewhere.
I have available to me Europtix
bolt-in HID kits that are bulb-specific. All you do is mount the ballast/wiring and pop the HID bulb into the H4 housing and you're done. I don't believe youll have high beams after this, but I doubt you'll care or need them anyways once it's done.
A friend of mine just did this on his Zenki S14. He used E46 3-series projectors and drilled some holes and mounted them right to the reflector in his housing, make a little box to hold the ballasts, and did the wiring. He was done in a day and it turned out fucking great.
I'd suggest again picking up a set of the H4 conversion headlights because they're ABS, not metal and glass like OE ones, so they'll be easier to modify. You'll have to find a set of HID projectors that you'll like/that'll fit into you H4 housing behind the lens.
Remove the lens off the H4 housing secure the projector inside replace the lens.
The back of the housing will have to be modified to accomodate the HID ballasts, and you'll have to make sure that the wiring/ballast position and everything still allows the headlight assembly to flip up normally.
Good luck post pics when you're done.