I was about to chime in, but my post would basically of been what swathdiver has already said.

The quad-gearbox (2 per side, one each corner) is definitely not something I would do, and definitely not with plastic tracks. If one stalls, the other engine will have to pull/turn the other engine over - the tracks are become the weak link then SNAP! Then theres all the stuffing around with 2 times the electronics and for what added bonus? No thanks, I'll pass