The water outlet to the heater is different from the one on my original manifold. That one had a two-way outlet on the top of the thermostat housing -- one leading to the bypass hose, the other to the heater. This manifold has only one outlet on the thermostat housing, leading to the bypass hose only. The heater line connects to a fitting in the side of the manifold, just below the thermostat well and above the coolant temperature sensor.
The heater-line fitting is a screw-in with an unusual thread size. After several hardware store visits' worth of trial and error, I identified it as a 3/8" FPT (flare pipe thread.) Using a couple of brass plumbing parts, I've assembled a new fitting and attached the heater hose.