Sorry about the drift, but I've done some looking around on the Moths range and fuel capacity.
Tank:
Filler Cap:
This front tank holds about 40 odd liters. Add that to the 80 liter 300 mile range in the top tank and It's highly unlikely it would make 500 miles. But then again, there would be more tank space as there is no passenger, so 500 mile range could be a reality.