Time to attempt another one that I think I've worked out. So..
English private prep schools and student car building projects are the connections here, as follows;
Rust AG: The Mini-based Silcoates Ascender 3-wheeler, made by students at Silcoates School (as below), under the tuition of Silcoates lecturer Les Brown (an authority on British specials, with a Specials book to his name, plus his excellent Rochdale cars book)
Arch 17: This one took some finding as it looked like a typical Yorkshire school, but hundreds to choose from! I've finally narrowed it down to Silcoates School in Wakefield, where Les Brown worked.
Extra m: This is the Abbey Cat, another prep school student car build project, created at the respected Whitley Academy in Coventry for the old 'BP Build A Car' competition for educational institutions.