The rack case consists of two separate parts which are screwed together with M4 countersunk screws. Both parts of the case (left and right) are available for 2x Pi 3B and 2x Pi 4B models. So you can combine your case as you like. In addition both sides are offered with an universal cutout for max flexibility.

Each slot provides a cutout for a 128x32 OLED display, a shutdown button and some status LEDs.

The right case also provides a mounting space for a Mean Well LSR-75-5 psu.

The left case has a cutout for a cold device connector like this one:

https://www.conrad.de/de/p/501637-kaltgeraete-steckverbinder-stecker-einbau-vertikal-gesamtpolzahl-2-pe-10-a-schwarz-1-st-501637.html

The design is super sturdy!

The covers are optional. They are not needed for stability.

For power connection between the raspberries and the Meanwell psu use these:
https://www.amazon.de/gp/aw/d/B079TL3G4P?psc=1&ref=ppx_pop_mob_b_asin_title

https://www.amazon.de/gp/aw/d/B01C5WI7QY?psc=1&ref=ppx_pop_mob_b_asin_title

https://www.reichelt.de/usb-c-stecker-auf-freie-enden-sw-50-cm-usb-c-awg22-50-p292506.html?&nbc=1

https://www.reichelt.de/micro-usb-b-stecker-auf-freie-enden-sw-50-cm-usb-b-awg22-50-p292509.html?&nbc=1

Print it with PLA oder PETG.