@MrCapri, I’m loving your build! The fact that you made so much of it from 3D-printed parts is great. Unfortunately, I don’t have access to a 3D printer for my own build.
Regarding your difficulties getting the camera firmly in line with the frames on the film: Maybe a vertical setup with the camera facing down could solve this issue. Given that with extension the lenses for capturing 8mm are fairly long, cameras more naturally face straight down because you can eliminate the leverage the lens has in a horizontal setup. Facing the camera downward seems to work great for my Raspberry Pi HQ Camera, but I’ve also found it to be the “much-easier-to-get-straight-and-stay-there” orientation when scanning 35mm stills film with a heavy DSLR.
But there are also some great scanners, both professional (Filmfabriek HDS+) and on this forum (build by @cpixip), that use horizontal setups and look plenty sturdy.