The car lives again!
Flushed the coolant the best I could (there's still a tiny bit of floaty stuff in the reservior) and primed the oil, and the car runs like the gasket never failed. I'll put some hours on it, then do another oil/coolant change in a few weeks time, and that should hopefully be the end of it.
Also, who wants a milkshake? Disposing of this stuff is gonna be fun...
