It is sometimes impossible to tell what the factory configuration was by
the model number printed (or stamped) onto the unit. The model number
designates a "family" of computers and has only one absolute requirement:
the first letter (M = Macintosh, A = Apple II, etc.). The other digits are
essentially random.
That last 5-6 digits in the serial number usually end with the model numer,
for example, F1234HYD34M5000. The M5000 is the model number.
In some specific cases you can figure it out, though: there was only one
Macintosh 128K, for instance. In your case, however, we can't determine
what the initial configuration was (which would enable us to discover the
Finished Goods part numbers, eventually).