1958 Porsche 550A Spyder, chassis 550A-0145. Photos by Pawel Litwinski, courtesy Bonhams Auctions. Lighter in weight than the Porsche 550 Spyder it replaced and blessed with greatly improved handing, the 550A Spyder was once described by driver Ken Miles as “the greatest long-distance racer in the world.” Just 40 examples were built between 1956 and…