This is an old post, preserved for reference.
The products and services mentioned within are no longer available.
Following on from the composite video conversion I did a few months ago on a Radofin tele-sports TV game, I have modified quite a few other TV games of a similar type.
TFW8b composite video buffer board, that seemed to work quite well. The power was tapped at the bottom of the board, the video from the point it enters the modulator section, and the audio directly from the chip output.