It’s easy to see why the Jaguar Mark 2 became so beloved, regularly filling vintage racing grids, auction house lots, car show lawns, and top-10 lists of the greatest sports sedans of all time. This is the original, after all: a four-door with the power and poise to keep up with sports cars, plus luxury in abundance. In post-War Britain it was a revelation. It still is today. Like many automakers in the Thirties and Forties, Jaguar was conscripted into supporting the War effort, but founder Sir William Lyons always had an eye on the future. The story goes that he and his engineers worked on a new straight-six during…