I am possibly completely wrong here but,..

I have a vague memory that the NSR250 front headlight was deemed too small to meet ADR specs back in 1989-90.
ADR stands for Australian Design Rules,.. again very vaque memory. Link
But I think I can remember some special Australian Edition NSR's came out in Australia with larger headlights to get around this law.
Possibly, that is what you have. Maybe the Australian Honda importer did some modifications to get the bikes legal in Australia?
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[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...