Kurt,
I was able to get heat from my B&B headers without the assist of the main engine fan or the assist motor in the engine compartment. I didn't have the crossover tube on the heat exchangers installed as shown in this picture:
http://hstrial-klehmann.homestead.com/files/MVC_896S.JPG
The only thing I had connected was the tubing that goes from the exchangers to the heater valves. Got pretty good heat. I'm sure the assist motors in the footwells had something to do with that.