I've used this SD Card extender: https://www.amazon.es/dp/B00ZUA2EYK
Other parts are just from the original model.
Changes was made in PrusaSlicer direclty - so I'm sharing resulting 3mf file.
I'm not author of original case, I only made some holes for fitting my Sizif-512 in case.
Original model: https://www.printables.com/model/700687-replacement-zx-spectrum-48k-case-key-caps-for-mech
The author remixed this model.
Holes on bottom part for fitting Sizif-512 computer