Mercedes 300 SLR on Goodwood Festival of Speed

There are precious few cars whose anniversaries call for celebration on Goodwood Festival of Speed four decades down the road – but this year is the Porsche 917's 40th birthday. On Saturday and Sunday, the Goodwood Festival of Speed marks the occasion with the largest gathering of 917s ever seen in Britain, including short- and long-tailed cars and CanAm derivatives. And yet,