Other than the Opel being built from bits of a real road car, it is
completely unsuitable for street use. The 376 mpg was not obtained on the street either- we are talking closed course, no stops, extreme pulse and glide, low average speeds. I haven't found specific info on the builders but I'm fairly certain they AREN'T Shell engineers as we are told. Shell SPONSORED econo ralleys, and they still do, but Shell doesn't enter their own vehicles, and I'm not sure when the last time is that any of their own engineers did.
The Opel is a purpose built competition car. Some of those mods could be brought to the street but many of them can't and the end result wouldn't be any better than what you guys are doing with current offerings anyway.
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Additionally, it appears to have a side draft carb fully enclosed in an airbox and it BREATHES through the crankcase ie: ALL the intake air comes through the crankcase, as well as being preheated by the "radiator".
Well if I wanted to "cheat" in an econo contest I'd make the carb breathe crankcase fumes, and fill the crankcase with 2-stroke mix. How much do you wanna bet that thing would run with *NO* fuel in the gas tank at all?!? LOL! Wouldn't surprise me to find two or three "hollow" cylinders in there either.