The 65-70 B-Body was something like the 4th best selling vehicle of all time, but that counts it as a shared model. We've seen there are a TON of differences between the US car and the Canadian car, but if you went even a step further, what's shared between a Catalina and an Impala for example?
If you took a Chevy, a Buick, and a Pontiac B-Body, what's common between them?
The Pontiac chassis is bigger and sturdier but older tech up front, so it looks like a different generation of chassis, but they're still body B-Bodies. Floor maybe?