Thanks for that insight on the earler 65-70 bodies, I can see where car design was changing to the long hood/ short trunk in that time period, so it seems they just adjusted the design to put the extra length in the front.
Also, I found a set of Fisher Body movies that have been digitized and uploaded to youtube, showing the construction of the body... it seems that the tooling to handled the entire body assembly was keyed to the dimensions of the main passenger compartment, that was probably also a consideration as to why that part of the car remained the same size while the front/ rear of the car could change.
The best video is titled "Fisher Body, The Body Builders"- this highlights the 1971 model car line for GM, following the design process starting in 1968, as digitized by PeriscopeFilms, at:
https://www.youtube.com/watch?v=yYgxgGlN8CM
There are other videos about Fisher Body, this next one seems to be the sequal to the 1st, about a decade later- from the 1980-82 time frame -cars highlighted include an early 80's Chevy Citation, Olds Delta 88, Buick LeSabre:
Title is: FISHER BODY GENERAL MOTORS AUTOMOBILE MANUFACTURE
https://www.youtube.com/watch?v=RAL5-B2ROkw
When watching these videos I was somewhat astounded (to my 21st century sensibilities) of just how much manual labor went into car production before the era of mass-robotics, and computer-controlled production- it was a bit surreal to see all the hand-sewn pieces being assembled into seat covers, interior upholstery, etc.. not to mention the multiple shots of engineers drafting on long drafting/ lofting tables.