Don, would you care to explain to me how the fuel is smart enough to just make a 90* turn from the front feed port, and go directly out the overflow valve without feeding anything first?
You do realize that the overflow valve has to have a certain amount of pressure to push it open to let fuel out, right?
If you are feeding from the front, and the rear of the pump, then when you turn your supply pump on(assuming the IP is empty), assuming that the lines are Y'd out and are the same length to the front and back of the pump from the Y, then the fuel is going to come in and meet between #3&4 plungers. Then, once the opening pressure for the Overflow valve is reached, some of the fuel from the front feed may exit out of the overflow valve, but it will still have a constant pressure in the pump and be supplying the front plungers because the pump will stay full of fuel unless you are running out of volume. The plungers do not go up and down all at the same time. So if any of #1-3 plungers are firing, the front feed will get fuel to them first. If #4-6 are firing, then the rear feed will get fuel to them first. And any extra fuel that gets into the pump(pressure) will go out the overflow.
Eric