in the engines or the cars ?
In the engines the 300 will have a different front end (quite possibly serpentine) and a plastic cover over the top, the oil filler is also in a different place I think (it's immediately behind the thermostat on the 200)
In terms of the actual vehicles (the face lift that went along with the 300 engine means that most of the discoveries are referred to as being a 200 series or 300 series irrespective of whether they have a diseasil in them) are most noticable in the headlight surrounds externally, as the 200 series has a plastic surround and the 300 series lights meet up with the bonnet.
On the rear a 300 should have indicators and lights in the bumper, a 200 won't
on the inside, a 200 has a completely different interior designed by a famous person [1] and has the radio in a silly position at 45 degrees next to the gearbox, the 300 has the radio in a position where it's flat and you can press the buttons from the drivers seat :D
[1] Ray Charles by the look of things
