So, you're saying the ESC won't fit forward of the motor? IF it will, it would work better to reverse the batteries, leads pointing forward, and connect the batteries with a "Y" so you will have the batteries in either parallel(longer run times, less speed) or series(more speed, less run time) as you desire. The shorter the wires, the less voltage loss and less chance of burning up a wire. Having the receiver in the back would be better, weight wise, since the receiver is several grams lighter, on average, than an ESC. You could move the motor aft a bit, giving more room for the ESC in the front as well. Is the ESC water cooled? That could make a difference in location as well