Here's my design for a FWD Prius with a 36hp VW engine with Type III cooling on a Superbeetle transaxle. I contend that within it's performance envelope (plausibly smaller than the stock Prius, but maybe not considering the weight savings) it would return equal economy.
I don't have it in my Albums, but at the NW Bug-run someone used to drag race a Rabbit pickup with a air-cooled VW drivetrain in the rear.