Half of the stuff isn't there at all. Either not needed (like an air compressor -- a lot of the older units use vacuum brakes, with an ejector to supply the vacuum) or headlights (sometimes) and therefore generators.
The main reason, though, is that North American roads often had an engine built, and then specified all kinds of add-on equipment -- or added it on later -- and it was usually put where it would fit. UK roads didn't do that; the engine was designed and built all of a piece, and looked it.
Both approaches worked -- but they sure did produce different lookings engines!
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