Gareth, I have never had a problem to undo the screws that hold on the rubber surround. They are quite deeply recessed but get a crosshead screwdriver in there, go carefully until you are sure you have the screwdriver in the screw head. The washers on the back of the surround often come off & you need to refix those, superglue or suchlike.
Undo the 3 small cross head screws holding the chrome trim ring (don't undo the slotted alignment screws by mistake), remove the ring & the candle power sealed beam units just lift out, unplug the connector.
Get the H4 conversion kit from one of the specialists, I got mine from James Paddock but they all do the kit. At the same time get a set of Osram Nightbreaker H4 bulbs, these fit straight in place of the H4 bulbs in the kit. They are the same wattage so will not take any extra current. I have done this on both my cars & it does make a difference. It is worth checking the beam alignment to maximise the benefit.
Clean the headlamp connectors while it's all apart. Dab of copper grease on the trim ring screws & the screws for the rubber surround will help any future dismantling.
Tony
<font size="1">1981 TR7 FHC Cavalry Blue
1980 TR7V8 DHC Jaguar Regency Red - sadly sold!
1977 TR8 FHC EFI Factory development car Inca Yellow</font id="size1">