I took a look at the specs for ya and it does work with composite video. Using pins A11 and A12 (GND) for the composite video input and set pin A19 to low (GND) or leave it open. This is outlined on page 10 of the datasheet on EarthLCD's site.
What the conversion board brings to the table is:
- a flex cable to connect the board to the screen.
- power supply regulators and pots to adjust tint, colour, brightness and contrast.
- a 9VDC adapter to convert 110VAC to 9VDC.
- an RCA jack for composite video input.
There is a whole circuit diagram here of the conversion board.
If you want to hook this to your car you can probably build a 12VDC to 9VDC regulator circuit (they're not hard).
Hope this helps.