I have searched for the answer to my question multiple times over the years (when I get inspired to search for the answer every so often), and thought I would just put it out there for input from other owners.
When I restored my 1974 2.0 many years ago (before there was much internet info), I had the door jambs repaired, and there was nothing to screw the door strike plates to. I fabricated a 1/4" solid steel plate that was drilled/tapped so I could adjust the strike as needed and tighten it to jamb (sandwich jamb sheet metal between strike plate and tapped steel plate). Has worked fine all of these years, but I always figured there may have been more in the original design.
I have found replacement angle pieces that look to get welded to the backside of the jamb and the unibody wall inside the rear fender, but still no idea what the strike was screwed into from the factory.
I am sure what I have is functionally correct, but probably doesn't meet side impact requirements (especially on the later cars with the impact beams in the door). Have found very little info or pictures on the internet. Hoping someone here can enlighten me as to how the strike plates were factory installed.
Jim