I recently had a problem with twin filament headlamp bulbs JC, trying to cross reference as the handbook 'helpfully' said to only use Ford bulbs !
Fortunately found some NOS Lucas at a sensible price
Also found some aerosol 'chrome' paint which has made a nice job of reviving the reflectors, which to my surprise originally had some sort of plastic 'silver' film sprayed or dipped on rather than the expected chrome plating.
In the end all but two of my bulbs, apparently originals from the ENFO mark, had working filaments, I was quite surprised given the amount of vibration, and particularly shocks from the tractor being driven at speed until pulled up by the chain or wire hawser hitched to a tree or stump, something it has done consistently throughout its life with us.