have you ever seen a 396 with a smog pump, how about a 402? additional components cost $$$ (the minimal increase in displacement was a cost consideration, a new block was not engineered)

in the mid-'70s 440s received smog pumps in CA (low production quantities) but was not required on the 400 (larger production numbers offset the costs bringing the new engine to production)

& to save costs, Chrysler Corp. wanted the new "B" engine to share its bore with the 440 at 4.320", but with the 3.375 "B" engine stroke that would've been 396 cu.in. (wasn't going to happen )

someone suggested "400 cu.in." sounded better & bore was increased to 4.342"