455, originally was designed as a large journal stroked and bored 428. It's not a derivative of the 400.
The 326 is an orphan and spawned no children. Originally meant to be 336 CID, the GM brass told Pontiac to make it smaller than the Chevy 327. There's a few year's worth out there marked as 326 which actually measure 336.
The 400 is a bored out 389. The 350 is a 400 stroke but smaller-than-necessary bore compromise. You can not bore a 350 out far enough to make a 400 without sleeving the block, at which time you ask yourself: "Why didn't I just turn down the mains on that 455 crank in the first place?" Olds thrust bearings to the rescue.
