By that same logic, a 332 isn't a big block, either. Or is it? IMO, displacement has very little to do with whether it's a BB or SB. The 351m/400 is an altered 335 family engine, designed to fit where a BB would also fit. IIRC, the 351m/400 use the same perches as the 460, too. It's a small block in a big block kinda world.