Well good choice on the adapter, you do not need any additional modification to that converter board, so get rid of the resistors.

Take the adapter off and if you have an arcade cabinet running RGB try and get a clear picture on the LCD using the converter board.  That way you can exclude what you think is just a RFM issue.

The stamp settings when not correctly adjusted give that tail appearance to SOME graphics and also can also affect the graphic colours.  Be prepared to sit down for a couple of hours and play around with the stamp settings until you have a clear picture.

Unfortunatly I don't have an arcade cabinet to test the converter board, so will try on rfm again