Took the car out for a proper drive a few days ago, and by and large, it performed admirably. Two action items: first, I have to adjust the brakes a bit - they pull to one side slightly and aren't as responsive as I'd like. Second, I've sprouted what I believe to be a coolant leak. That's being worked on now.
In addition to that, I shipped the radio off to a guy who specializes in classic car radios - I plan to have him repair the AM equipment so that it functions stock, and add one of those drop-in "ghost" FM chips. That way, I can return the radio to original condition at will, but I'll also have FM, which is what I mostly listen to.
Then I also ordered a replacement "Pontiac" script for the speaker grill, you may remember that was missing. It didn't come with the clips to hold it in, so I 3D printed 3 ring washers out of some rubber-like filament, and those hold it in admirably.