"really extended motor life."

It must, I bought a 1978 Suburban with over 90,000 miles on it that was run on propane.  They switched to regular gasoline when the propane ran out while pulling a van.  They didn't move the distributor back though and melted a piston.

I took the engine apart and it looked almost new inside, clean and no apparent wear.  I called the owners to find out if that was the original engine and it was.  I've seen small block Chevy engines with less than half that mileage look all sticky and filled with sludge inside.