I hooked up the heater core, so now that I don't need it anymore because it's getting hot again, the heater works.
There's a T-fitting which attaches to a 3/8" hose which goes to a built-in oil cooler. I couldn't get the 3/8 hose which I needed to replace it (it has a sharp 180 deg bend in it), so I just ran a longer hose in such a way that I didn't need to bend it sharply.