There are several examples of off grid people mounting a gas engine (think riding lawnmower size) to a high output alternator. They (usually) call them DC generators. Assuming fusing at BOTH ends, go for it. I ran 4/0 for my inverter charger - both ways.
Most high output aftermarket alternators are close to 50% output at idle, VS closer to 20% for small stock alternators. I think the 16 HP figure is a bit high, 10hp at full output seems more reasonable. The AC compressor pulls a significant load on the engine and cooling system, with no ill effect (other then mpg's).
The solar is a good idea, but 500 watts at 14.4 volts is a whopping 34.7 amps theoretical max at the panels, real world closer to 25-30 amps at the batteries, less if it is overcast.
