Ken Fry seems to know what he is doing on the drivetrain. The genset in The Zing! weighs 49 pounds, plus a little more for the fuel tank. The engine he has in the POC is 25% efficient, and I think he said they will get ~32% efficiency in the production units.
See post #3:
The Zing! - ApteraForum.com - Unofficial Aptera Car Forum with more info throughout the thread.