Jaguar's racing dept made 2 Mk VII bodies of magnesium in the mid 50s, shaving 440 pounds, and one still exists because it was saved from the junk pile by the Jag PR director who mounted it on a car and went racing.

 

https://www.goodwood.com/grr/event-coverage/goodwood-revival/interview-rowan-atkinson-on-racing-his-remarkable-jaguar-mark-vii