[drummond93]

As for the difference in length between Catalina and the Bonneville/Grandville, here's what I've observed and learned from personal examples of each, cross-referenced with the 71 Assembly manual and the repair guide and parts interchange books for all 3 versions:

The GM B-bodies were required to have the same interior dimensions across all product lines, so the dimensions from the firewall to the rear quarter panels are the same- this was mandated by all cars having to use the same glass for windshield and doors. (this is referenced in another posting somewhere on the forum, apparently the window glass molds were prohibitively expensive to change, they were the single-most costly item to change between models- which is why the interior never changed dimensions even if exterior length did. External door skins may have changed, but the internal structure of the doors are always the same across the entire GM B-body line. I've not come across any reasoning for modifying the length to begin with, somewhere an accountant must have signed off on it, realize they were still changing significant parts of the body sheet-metal every year still to allow year-to-year model changes.

For Pontiacs B models, the rear quarters are also the same length, even thought they were changed slightly around the rear windows due to the different rear glass (as mentioned previously, the Grandville had it's roof line and rear glass sourced from the Cadillac D-body) with the taillight panel also changing between the Grandville and Bonneville/Catalina.

Forward of the firewall is where the changes were made; fenders were shorter on the Catalina; however the hood stayed the exact same; to accommodate this this the Catalina front header/nose panel was shortened and partially indented about 3 inches to allow the hood to sit closer to the headlights and bumper. -I think it also meant some modification of the bumper mounts, as well. I'll try to get a picture of what this looks like and post it.

I'm still amazed that Pontiac engineering designed it this way; it required new metal molds for stamping out 2 different L/R Catalina fenders, plus a new mold for the fiberglass header as well- all of which are barely noticeable and seemingly of little importance for the overall model design (the rear roof line and resulting change to the rear qtr panels were much more noticeable, as stated earlier to distinguish the Grandville as an entry closer to the Cadillac.