I had two problems with headlamps.  The first was that the metal cowls that held the bulb in place were completely rusted through. The second was that no amount of sticking things to the US lamp would divert the beam to the left.  It failed the MOT on both counts.

One cowl (which holds the lamp in place) was completely knackered

It just fell apart

The other was a bit better. Plan was to use this as a mould - the two cowls are symetrical

Use plaster of paris cloth strips to make a mould from the original

Lay clingfilm and then glass cloth and epoxy on the outside of mould to create a copy of the original

Spray and you have a copy made of the original metal cowl

Two screws with adjustable nuts hold the cowl in place and allowm you to adjust headlamp direction

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Luckily I discovered (due to the power of globalization) that International School buses use exactly plug compatible headlamps as a Daithatsu Fourtrack - which you can buy on eBay with a UK left side beam.

Headlamp for a Daihatsu Fourtrack (left hand beam)

Still functional