Hi, recently done mine and first of all it really is worth the grief and hardship, they look fantastic.
Remove the light unit by unplugging all connectors to the rear, don't worry they are all different and can't be put back wrong.
Once out you need to bond the ballasts to the front bodywork somewhere near the headlight unit so the cables still reach. Whilst they are bonding you need to prepare for removing the clear front lens off the light unit. I used a large wide screwdriver.
To do this you can either warm the units in an oven as some suggest but it works really well with an hair dyer on full blast and moving it across about 4" at a time. After about a minute and of coarse unclipping the metal clip retainers you can start placing the screwdriver head in between the two plastic parts (one black and one clear) and slightly twisting the blade. If the temperature is correct then you will start to see the original bonding material start to stretch like chewing gum and you can continue round still maintaing temperature with the hairdryer until it pops out. While the bonding material is still warm I pushed any that came out back in as this can be used again when replacing back the lens.
You will need to drill a small hole in the black cover to allow the cables to come out. I placed mine strategically at the top and out of the way of any fowling parts. (this can be siliconed afterwards).
Beware of placing the rings to low on the headlight unit as when you close the two back together you may well find that the bottom of the rings will fowl on the two pieces coming together.
You will need to run the hairdryer around the unit again prior to clamping them together again and don't forget the metal retaining clips.
You can run a small bead of clear silicon around the units if you want but mine was fine as I ensured I got the original bonding material warm.
It took me about 50 minutes for each light unit and forget latex gloves as the black bonding material loves them and won't let go. keep some paint stripper handy to clean up afterwards.