Are you looking for complete headlights with ECE markings or just LED bulbs to replace the H4 bulbs.
Havent seen complete LED direct replacement headlights assemblys for the GT40 to replace those square Marchal units.
You could opt for LED replacement bulbs but they mostly give a wrong light pattern when used in a H4 or H1 headlamp or spotlamp assembly which will fail MOT.
The other reason for sticking to regular Halogen bulbs is heat. Heat evaporates the moisture that gets trapped behind the covers.
I did some testing with my lower spotlamps (FoMoCo).
Test one, H1, standard 55W Halogen bulb
Test two, H1 Rally 100 Watt Halogen bulb,
Test three, H1 LED replacement bulb, (advertised as H1 6500K WHITE COB LED 36W 8000LM)
I went for 55/60 Watt H4 bulbs in the headlamps and 100 Watt H1 bulbs in the lower spotlamps. All switched through relays so all power goes to the lamps. (direct 12 Volts to the relays & relays got switched by the switches. No loss in power to the lamps = more light).
The lingo for LED is Lumen. A regular H4 bulb does about 1800 Lumen and about 1700 Lumen for a H1. Lumen is the amount light produced.