Ok I have being working on the RGB to Composite converter today and have found a connecter inside the atari 1040STF that has some pins that are connected to the din connector used by the Atari monitors. I have test all the pins to see what ones go where and have found that 7 of the external pins are connected on the inside of the ST.
So all I really need right now is a pin out diagram of the Atari 1040STF video connector on the back of the ST. This would be of great help to me and to the rest of the Atari ST community as I will publish all this info on my homepage when the project is completed.