I don't think cross beams will be needed, with 6" wide supports on the front and back, I doubt it will bend much. I tried to do an FEA of it to test how much force it would take to bend the frame but my computer crashed.
Low motors shouldn't be a problem, as long as the wires are routed safely, besides they are .666" (interesting number, not by design, but curious nonetheless) off the ground, the angle of the picture is a bit deceiving.
If there are ramps in the competition, the trannys can be inverted, but they stick up pretty high, thats why I have them down.
Arefin, we don't need to talk, you know you love this.
Thanks for the questions!