Presumably the description that "mirrors were used in a periscope like arrangement" refers to something like these: https://www.keslowcamera.com/gear/lenses/other/periscopes-an... or https://www.panavision.com/camera-and-optics/optics/product-...

I once played with a sub miniature version of this with a 35mm screw adapter. I think it's the kind of thing used to shoot inside violins, or the one I saw architectural models.

Bigger would admit much more light for film