Mr. FancyPants.

The difference between the US and Euro round
is that the US round are sealed beams and the
Euro round are mirror and bulb type, just like the modern
cars have now.
So you can change the bulb with a simple twist and pull,
instead of changing out the whole ackward US headlight assembly.

And If not mistaken, the earlier Euro 280's came with the
rectagular ones and all other Euro w123 came with the
round ones.
Later models all had the rectagular ones.

Could be wrong, though.

Louis.