SS/B Barracuda project
The steel on the door I was shown was paper thin. The paint looked thicker than the steel and very rusty orange inside. Very convincing to me of acid dipped parts.
The owner of the car was particularly careful while opening and closing the door when showing me the metal thickness. The door and window parts were lightened to the point of easily damaged if treated as production parts.
I never looked at the bumpers up close myself but I like the double sheet stamping idea mentioned above for them since they required chrome plating. Acid milling does not leave a smooth surface thats needed for chrome plating.