You would be better off with a point source light as you are trying to project something and the diffuse
reflector on a scoop would take all the detail out of the image. The original
Linnebach projector was a point source light in a big metal box which you would put a large transparency over, thus projecting a background. (Later units worked more like a regular projector with a
lens)
If you had an old scoop that you didn't care about, you could paint the inside with flat black stove paint and put a small filament quartz lamp in it. You would need to suspend the transparency slightly away from the front to reduce heat buildup. Good luck!