This 6c 2500 has been lingering on the Internet for years since about the year 2005 and was primarily assumed to be a Boneschi creation as previously stated in this thread. Links to the designer Michelotti were also made.
In the 2017 wonderful 2-volume books "The Encyclopedia of Italian Coachbuilders by respected author Alessandro Sannia (one of the forum members here if I'm not mistaking) it is listed as a creation from the short lived Milanese coach builder Taglioli & Granata.