Here you are the truth about the so-called Facel-Vega HK500 by Zagato (or HKZ or HK500 S).
Bertrand Osio is a member of Amicale Facel Vega (now vice president of the Bureau Exécutif) and used to draw posters for the Association's bullettin. In an article dated April 1 (April fools day) he reported the discovery in the States of a HK500 coachbuilt by Zagato. There were 2 drawings in that article (there couldn't be any pictures of course...).
Later, the British owner of a wrecked HK500 began a restoration. In that occasion he decided to realize Osio's version of a wannabe Zagato's Facel Vega, removing the original engine and replacing it with a modern Chrysler unit of 8.2 litres developing 575bhp.