Tony,
Basic question back at ya:
Are you going up to the viewer window and making sure you are at a 16:9 aspect ratio. Even if you are encoding at 480×270 if the preview window is showing 4:3 you will get a 4:3 video.
When I bring in DvcPro hd 720p it gives me an auto custom aspect of 1.7778. But, If it is giving you a 4:3 (1.33) switch it 16:9.
Also try using unconstrained aspect when editing a new preset.
– Dane H