So, that was anticlimactic. HVAC guy's done! He just yelled up the stairs, so I went down and he showed me how he'd done a couple of things, and said that when we get the drywall done in the corner where the return is he'll come out and make a metal sleeve so it reaches to wherever the drywall winds up being, and I told him we'll work out when we're going to get the upstairs demolition done and give him a call for that part.
We have heat! And air conditioning! And it works! OMG!