Gordon, I think a typo has crept into this thread. XJ516 was a Sea Vixen, the Sycamore was XG516.
The usually reliable Britains-Smallwars site has no RAF fatalities showing for 18/02/57, the date of XG516 accident. It has two showing for XJ896 (10/02/58), and a Royal Marine killed in the XG546 accident (31/05/57).
A Sycamore(XF268) "rolled down" Mount Olympus on 08/07/55, but no fatalities shown.
Four RAF fatalities (1 x Flt Lt, 2 x FOs, 1 x LAC) shown on 08/07/57, but I have yet to find an accident reference.