In the course of my travels, I read about the K5GNA dish screening on K5OE's site:
http://members.aol.com/k5oe/K5GNA_dish.htm
According to the text you get 1.5dB from the screen.
As far as the 1.2GHz antenna, I've only got a couple responses. No real clear answer on whether linear or circular is an advantage, or if switching polarization is advantageous. Not sure if this info is so common no one is interested in answering, or if there are so few users of the mode, no one really knows. Nothing on the AMSAT site I could find. Individual web pages on the topic yield a vastly disparate range of configurations, so no clear path to follow there. I got a quantative value of 1kW ERP on 1.2 to work AO-51, and a source of yagi antennas from M2 and helix antennas from W7LRD.
Mark K5LXP Albuquerque, NM