So for those unfamiliar with the current flow:
Blue line goes to upper rad hose.
Yellow line goes to the heater core intake line.
Orange line is the return from the heater core which has technically seen a heater matrix so slightly reduced in temp from that.
Green line is to the lower rad hose.
What's been changed from stock? The throttle body heater line is deleted. No biggie. BUT there's also one less line to the thermostat housing. You can see it's now blocked off next to the orange line. This line would normally go to where the yellow line comes out of the intake side of the head. The heater core line would have normally come from the neck on the back of the head.
What I'm suggesting is to add the fuscia line below and add a port on the rear neck for the heater core line. This is what the stock configuration was using essentially just snaked around in a different manner.
Or this which I think is more correct on flow pattern:
