That would be a rather long chain, I guess...
The one I created at my first attempt was even longer
GAZ Volga M21 and Scaldia Volga – same chassis
Scaldia Volga and Beardmore Paramount Mk VII 1958 – same engine (Perkins P4C)
Beardmore Paramount and Bentley Mk VI Sports Coupe by Windovers 1947 – same coachbuilder
Bentley Mk VI Sports Coupe and Bentley Mk VI Drophead Coupe by Chapron 1950 – same brand
Bentley Mk VI Drophead Coupe by Chapron and Citroën DS Le Dandy – same coachbuilder
Citroën DS Le Dandy and Citroën AX – same brand
Citroën AX and Aixam Mega Tjaffer – same engine
A shorter one, in four moves:
GAZ M21 and GAZ M24 D – same brand
GAZ M24 D and Peugeot 504 Diesel – same engine (Indenor XDP 4.90)
Peugeot 504 Diesel and Peugeot 106 – same brand
Peugeot 106 and Aixam Mega Tjaffer – same engine