After running Sprint then Metro 1.0Ls on my 2150 mile commute since 1987. I’ve looked at almost every conversion from natural gas to burger grease. The Metro’s original design is pleasing and economically unique so it will let you cruise right past today’s complex world of auto company, political, and energy industries manipulation at the most reasonable cost.
In addition to artificial manipulation the forces of supply and demand for fuel by its nature will bid up alternative fuels so if your 1.0L consumption is low it’s your best defense burning any fuel. You already have tremendous economic advantage over the old 1940s design guzzlers. Watch Archer Daniels Midland (ADM) they are a lobbying powerhouse and the largest producers of Ethanol they seek large profits.
I did go after one Metro conversion and still regret missing. It was at Fathers Joes auction in the early 1990s. (Father Joes is the huge auction for cars donated to Catholic Charities in Nevada, California and Arizona sold to Mexico) I found a conversion by an engineer in Arizona, the back seat and luggage area nicely converted to hold batteries. Rear wheels were run by small electric motors his spec sheet said batteries would power the Metro to 55 mph for 70 miles or you could reverse with a pedal switch while downhill or running the gas 1.0L engine and charge the bank of batteries. It bid way past what I had to $12500 at a time new Metros sold for about $8 to $10k. Still wonder if it was capable of 75 maybe even 100 mpg?
Before undertaking any conversion, and risk your car, or put thousands dollars in time and money converting only to find a marginal gain study the options carefully before opening the tool box. Any fuel we burn has complex global pricing pressures so the low consumption of the 1.0L is still your best way slip right past the gotcha boys.