I also attended the Antwerp classic car show a couple of weeks ago Delorean, and like you, I spotted the strange Lancia-Mercedes coupe cocktail, and took some almost identical photos.
From what i understand, c.1960 the owner of the Aurelia B20 - a Brussels-based pharmacist - suffered mechanical problems with the Lancia, so swopped its running gear for the stronger and more reliable Mercedes-Benz 220 to make a rather unusual marriage.