Just go around to comparing the front panel where the headlamps mount on the
200 and 300 discos...all the external gubbins including wing shape vs. indicator/grille shape appear the same, and should be interchangeable - the indicator mounting may differ.
BUT, the big one. The headlamp mountings are different - the panel on the
300 has a much larger hole for the lamp unit and completely different adjusters. You could no doubt chop around at the 200-type front panel to get the headlmaps from a 300 to fit, but it's not trivial. The hole is about 1" larger radius (at a guess) and the mount/adjuster things on the 300-type lamps have a cunning hole each to locate into.So it can be done, but is more than the 10 minutes' work it appears to be at first sight. It's also likely to be irreversible once you start chopping the panel up, so when you get it wrong you'll be in trouble as I suspect the panel is welded in to the front of the body, so changing the whole panel would be a non-trivial task.