Block heater installed. Got under the car and looked, and realized I could get to it from above. It's right next to the catalytic converter on the back of the engine, and is removed with a 1/2" drive.
With one hand I unscrewed the drain plug, and with the other I pushed the block heater into place. All said and done, I lost less than half a cup of coolant. Torque for the block heater is 44 ft/lbs, and it takes a 24mm socket.
Now I have two plugs hanging out of the front grille, and they'll be attached to a light switch by my front door. Will probably flip it on ~2 hours before my wife heads to work.
EDIT: Updated first post with a picture glossary