I'll take the opportunity to sum-up this puzzle and add some clues.
Unfortunately when I broke my HD, I lost some few info...however I've been able to find back some bits:
et1: Still out there, being restored by the company that still bear his name. (I had a pic but it's gone). Not a totally obscure name because he is featured in several books (2 of them by an Autopuzzles' member), but not for this 750 sport..
et10: This one has many points in common with the one above..it is still out there (pic will follow), the builder is featured in one book by an AP member for a different kind of car and they are from the same place (more or less 40Km) and their names end the same way too...but this is a 1100!
et13: This one is featured in Curami's book, but in a different form. He built just this 750 but not Fiat based.
et16: I lost what I found about this, but I've been able to recap...the car is called Xxxxxxxx 1100 (except for 1 letter too much, it's just the same of a better known etceterini) and the pilot is Dixxexrx.
et18: This 1100 was built by P. Oxxxxxo.