Unfortunately I cant show the photo, but the center is definitally a tube in the front, not sure about the rear. I was shown a high res photo that showed the tube running up the center. Which also makes me believe tht this is some sort of a mount, with a screw down the center on one side, mounted to a metal mount like in the photos above.
Im sure youve all seen them, they attach to rods, and have a screw that goes downn the cetner and 'bites' into whatever its attached too.
Im wondering if theres some photography equipment used to hold the heiland tubes or something, that looks like this.
The top sash is what the mounts 'clip' to, so the thickness is determined by the scope mounts. If the scope mounts were further apart, the sash would be thicker. Does that make sense?
I cant say the scopes that everyone says are 'acurate' arent acurate, but im sure the modern mounts are not quite acurate. But your correct. And the holes do need to be drilled. I dont think these are more than 70% acurate really. But for molding purposes (simplicity) and rough acuracy, i think they are getting close.