The first time I had to replace a blown headlamp bulb, the guy in the (local) shop didn’t have/couldn’t find any original 45/40watt R2 ‘no.376‘ bulbs (on the left in the picture) so he sold me 60/55watt H4 ‘HBU12‘ halogen ones instead (on the right). I’m glad he did - they have a brighter, whiter light than the original ones, although a few pounds more expensive. I’d recommend all owners to fit them.
Apparently, the same headlight units were used on the Triumph Acclaim saloon car from the late 1970s - the product of a joint-venture between Honda and British Leyland* - worth remembering when you’re in a scrapyard.
*Under 30s, ask your fathers.
Alternatively, I’ve been told that the headlamp units from a Bedford/Vauxhall Midi van can easily be substituted for the Rascal ones - this will allow you to use the more widely available fitting halogen bulbs.