e30 led headlight retrofit?

That would be something cool and unique. I will say though, you can always retrofit and get a pair of something similar to this: https://www.ebay.com/itm/300ZX-Z31-1…IAAOSwxxVb2z1b
The Zenki headlamps are generic lamp sizes (the whole lamp gets swapped not a bulb, can find them at auto stores); there are quite a few chinese manufacturers that make plastic housings, so you can use bulbs, that you can crack open if you stick them in the oven on warm. Then you just shove projectors and halos inside them. look up the owner "edicer" he's got them installed.

Zenki headlights are the same as the 1980's jeep cherokee

Problem with koukis are that the housings are Nissan and made of glass so you're SOL in modding them to have halos inside.

I would also say, just remove the glass housing on your Z and measure the mount points to see if you can find one of those halo kits for BMW's that would fit with some drilling.

How can I power the headlights? Would it be easier to wire up a switch? I’d prefer to keep a stock wiring setup

Seems like a lot of work. I took out the old housing and replaced years ago with new ones that could just accept new bulbs and in put in PIAA lamps, made a big difference. I think the housing was made by MOOG if I am not mistaken.

Nope, bake them at 200F for about 20min. The glass lenses are glued to the metal housings with seam sealer and can carefully be separated when hot/soft enough.

Clean off all the old seam sealer and reassemble with new seam sealer once your halo rings are installed. I just did this with some JDM zenki headlights that are a replaceable 9004 bulb like the kouki housings.