I have just released version 3.15 of Star Fighter 3000, which adds an option to scale the display to 320x480 when running in full-screen mode. This prevents letterboxed (or postcard) display on VGA-type monitors.
I gave up trying to persuade my monitor to display a 320x512 screen mode properly. It is a shame because that mode would have eliminated all visual artefacts of scaling, being exactly twice the game's native vertical resolution.
You can download a patch from the usual place:
http://starfighter.acornarcade.com
Christopher Bazley