Another option would be to create your comp in an HD comp, but center cut it, black bars on each side.
The best thing to do,= is call the people with the projector/screen and ask/talk with them about what deliverable will provide the best display BEFOER YOU START. They might say 720×486, 720p, 1080i, thing is you won’t know until you ask and you might end up doing work that will need to be redone because it doesn’t work for them.(sadly I speak with WAY too much experience on this issue.)
Johnny Cuevas, Editor
Thinkck.com
“I have not failed 700 times. I have succeeded in proving that those 700 ways will not work. When I have eliminated the ways that will not work, I will find the way that will work.”
—THOMAS EDISON on inventing the light bulb.