HID head lights

[beetle1303]

Its about time to bring back an old issue...
I know how HID systems work but i cant figure out if they will work correctly with the stock (seales beam) or with the clear lense headlights on a 1973 super, because of the small cap both headlamps have (where the tip of the bulb sits behind). Factory HID as the Audi A3 the headlamp has a small lense.

Can anybody explain the difference??? Im really confused on the headlamp technology and Im getting pissed off.
Can I fit an upgrade kit (single or Bi-xenon) to a normal headlamp or i will have to retrofit parts of an A3 headlamp unit for example into an original super headlamp?

Chris