I think you will find that the fixed lights were replaced in the field by adjustable lights at some point and the factory was directed to make the change on the aircraft it was building. Even then, I have been told that individual pilots had their crew chiefs move them to suit their taste (seems that no matter where you put them, there is still at least one instrument which can't be seen). The use of these lights tended to fade after technology allowed the lighting of each individual instrument (eyebrow lights) although it seems that a few remain in use in military aircraft, largely as a back up.
The lights themselves are rather neat. You can change from red to white (ever try to read a map under a red light - won't work) and back. The beam could be adjusted from flood to beam by adjustment of the front lens and in some cases the light can be removed from the mount and used much like a flashlight.
If you can't find a reference photo and still want to install them, you won't be too far off by installing one on each side of the cockpit, just below the point that the fixed portion of the canopy meets the fuselage, angled inwards towards the instrument panel. Install a third light on a post just to the pilot's right (and maybe a little behind him) at about elbow height. That would light up the right hand console, which usually contained the electrical switches and radio controls.
As on who has shot at least one landing (in a 172) holding a Mini-Mag in his mouth (cause the cockpit lites shot craps 20 minutes earlier), I would almost give you a 100 percent guarantee that no pilot in his right mind would remove his cockpit lighting and then go flying at night. Move them around yes, remove them? No way!