Convert your vintage Vespa, like a 1951 Vespa 125, into a battery-powered machine with a conversion kit from Retrospective Scooters. (Piaggio Group/)London-based Retrospective Scooters is offering vintage scooter enthusiasts a way to bring their rides into the 21st century with its Project E conversion kits. The Project E kits allow riders to swap out the old gas-powered components for an…