Actually the sedans, (at least the four door ones) did NOT have aluminum door frames. It would have been great if they were. They wouldnt have rusted then
They also dont have bumper guards either on thier bumpers..
As for why the Kadett.. See attached
Picture is Circ. 1985
Yes.. the Opel Virus hit me in High School.. and the car that infected me.. a 1971 Blue Four Door Kadett
Charles