Overthrowing Neutral to 1st/3rd could be avoided with a Lock Out type deal on each shifter (maybe). Something similar to a Ratchet shifter setup, only it would prevent throwing into a gear until the lever was lifted for a shift. Who knows, it's something to ponder.
Actually shifting it (provided the chance of overthrowing past neutral could be eliminated) wouldn't be hard. Can't be any worse than the '55 Dumptruck with a 4-Speed and 2-Speed Rear that my grandfather owned. (up until about 2 years ago when he got rid of it). That truck was actually pretty fun, and confused people my own age when it came time to split gears...for each gear. :D
Had I known ahead of time what my grandfather would have got in scrap weight for the truck, I'd have bought it from him and dropped a regular stepside bed on it to make a rod-truck.