I don't believe for a minute that fit and finish were not a priority. I have examend enough original unmolested vehicles and spoken with ex GM plant workers to buy that.
Poorly fitting doors, just for example leak water and whistle. Both are warranty items that people paid attention to and dealers didn't want to deal with then, same as now.
I'd say that it's more likely, that 40+ years of work and slamming and tweaking are why our doors that may have been hung on several vehicles usually don't line up perfectly.
