The longer hoods are NOT, in themselves, for the purpose of better cooling, though a larger radiator is usually included. It's so that the larger engines (ISX Cummins, 60-Series Detroit, C15 Cat, etc) will physically FIT in the space. They're looong! You usually won't find these engines in the shorter-hooded Class 8's, only the M-series Cummins and C-10, C-12, and C-13 Cats.
BTW, the Freightliner 112 is just that, 112" BBC. That's why it's easy to know FL BBC's. Just look at the series #.