Airbus codes denotes in the first number (in a -232 I mean the 3) the engine manufacturer, and the second is the thrust configuration.
Boeing codes note tho whom the plane was delivered. If a 747-100 was delivered to Pan Am it would be 747-121, being the 21 the customer number for Boeing for Pan Am. An Aerolineas Argentinas 727-200Adv is labelled 727-287Adv (AR's customer number being 87).
They're completely different methods.