Okay - so I chickened out. I hired my contractor (the one who built the Faraday run for me) to help with the conversion. I'll post pics as we go.
So far, I've got a nice big opening framed in and covered with hardware cloth and a door, so there'll be lots of ventilation in summer. (I've also got vents to add up at the roofline.)
We decided to cover the floor with more hardware cloth and the edges of the coop will have 2x2 (ripped 2x4s) along all the walls to hold it, to keep out rats. Last night the girls stayed in the new coop. And one of the girls is in the nesting box now. (Pics *after* she's done - don't wanna disturb laying.)
So, it still needs a proper roost (to replace the plastic shelves I made them sleep on last night) and a proper nesting box; a tunnel to the Faraday run, and then I get to put down the woodchips. Pics soon.