A: It has a valve outside the firewall and I've seen the hotwater return line go to the intake on the back of the driver's side, then it comes back out at the front and down into the waterpump. If you plumb them so they are parallel then the intake may get too warm and vaporlock?
It shouldn't... water will flow through the manifold 100% of the time, less volume when the heater is on full-hot. Which is basically never here!