[north]

That explains it very well, thanks!

The situation in 65-70 was exactly backwards. The interior panels (inner doors, door jams, roof, glass etc was common to all B cars from Pontiac, Chevy, Buick and olds (as opposed to C cars which were Cadillac as well as the Buick 225 and olds 98).

The way the made the extended B’s for 65-70 Pontiac was by lengthening the frame by 3” just before the rear axle and 3” (4” in 65-68) after the rear axle. All the extra length was in the trunk. The quarters were 6-7” longer, the outer half of the rear tubs were the same as the Catalina but the inner half of the rear tubs tubes are “canted” so they align with the Catalina body floor pan and trunk hinge structure. The trunk lid is also 6-7” longer than the Catalina version. Bumpers and tail panels dimensionally interchange other than decorative trim variations. Btw, this was basically a continuation of the same pattern since the first extended deck Star Cheif in 54.

Where you can see this best is comparing the way the frame follows upward the passenger floor pan at the rear axle hump as seen with a rear wheel removed. If you look at a 69 Impala the frame is just about touching the floor pan as it kicks up for the axle. On the Catalina the gap between the frame and floor there is 2” further apart. The exec-bonnie frame is another 3” further. Leaving about a 6” horizontal gap between the floor and frame.

In these long wheelbase cars the gap was big enough to be unsightly without skirts so executives have a clip on rubber filler piece so you can’t see through the lower car side to side. They didn’t bother on Bonnevilles since they came standard with fender skirts.

Another odd variance on B bodies in 65-70 is that Chevrolet B’s had the front axle located 1” closer to the O line (the vertical face of the cowl on the engine side) than on the BOP B bodies (Catalina-Bonneville plus LeSabre and 88). I wonder if the 71 Catalina continued this process or if the Catalina now had the same axle to O dimension as Chevy?

By the way given the success of the 69 GP and the 70 Monte Carlo (both which had their unique look from a wheelbase stretch between the front axle and O line) it’s not surprising that Pontiac decided to apply a bit of that magic to their New higher end 71 big cars. Also since the 65 Mustang the long hood short deck look had been king making those 65-70 long deck Bonnevilles look dated even when new. Look at the 68 A bodies compared to the 64-67’s, they chopped at least 6” off the rear and tacked a few inches to the front overhang for the same reason.

Perhaps the need for re-engineered 5 mph front bumpers and general cost cutting brought an end to the two wheelbase Pontiac B body in 73.