In the monitor section as the first or second modeline:
Modeline "1024x768@49" 50.63 1024 1056 1248 1280 768 784 790 807
and in the screen section add as the first or second mode:
The above modeline was generated using the Xfree86 Modeline Generator located here:
It says 'use at your own risk' but it's doubtful there would be any harm done if an older projector didn't like it. It did after all ask for the 49hz rate.
You will also need to change the VertRefresh range for the device from '50-70' to '49-70' or the server will reject it.
The X server may or may not actually select this mode automatically; that would depend on how 'intelligent' the LCD projector is, and whether it conveys to the X server that it would like to use this resolution/rate.
You may need to remove/comment out the other modelines if it does not get selected automatically.
I don't personally use modelines, so I can't give much advice further to this.
However, to do it the 'other' way, simply use something more like:
In the monitor section:
..and in the screen section, use only:
Best of success!
PS - though it could be a slight pain, you *may* find that you WILL need to comment out modes which you do not want used, if the desired mode does not get chosen. Another option would be to have multiple xorg.conf files, depending on what particular model of projector is being used at the time.
It's a small nuisance having to edit/rename xorg.confs and restart the server when changing projectors, but might be a necessary evil. I don't know another way to do it easily.