LPG or Natural gas is a great idea if you like cylender pressure spikes and torque loss.......its VERY hard on motors and i personally would stay away from LPG as a fuel....
LPG (or natural gas) burns way hotter than diesel and doesnt burn as long, but it burns hotter when it is burning. Therefore it doesnt push the piston down as long as diesel (the torque loss) and it has way higher cylender pressures (due to all of it burning so fast). I didnt look into the kits you guys have listed, but im assuming they are just an injection nozzle into the cold side of the CAC system. If the system malfunctions at all, you also would have more potential for a runaway than i would be comforatable with as well.