I've done this conversion a couple of weeks ago I've got a 92 200TDI which had crap headlights and I had a old 300TDI which was going to be scrapped so I thought easy just swap them over with the grill etc only take a hour
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how wrong can you be!!
The headlights and indicators on the 300 have different fixing points etc and different wiring connectors on the indicators and sidelights the way round I found was to cut the headlight mountings out of both vehicles and refit the 300 into the 200 and spot weld it in and used the fitting connections from the old 300 to wire the sidelights, indicators and fit the grill plus the trim in took about 6hrs to complete but well worth it.