Summary

While looking at Octo duct I realized I wanted one for my RPi4, but noticed the IO ports were in the wrong places. Then I looked around for an RPi4 OpenSCAD case model to adapt and found Raspberry Pi4 Sheath Case (SCAD). Then I found Raspberry Pi 4 model B OpenScad model
and realized I could add some features to provide clearance for the IO connections, and use that to carve an RPi4-shaped space out of anything else.

Please find attached a remixed OpenSCAD file with added IO clearance features, and a couple STLs, including a block and a sphere with a Raspberry Pi 4-shaped hole differenced out of them.

For example, the skull-rpi4.jpg file was created in PrusaSlicer by plating the Low Poly Skull https://www.thingiverse.com/thing:906562 and Plater/Right-click/Add Negative Volume/Load RPi4board_shaped_hole.stl and then juggling around with the scales, rotations and translations to make the RPi IO ports line up with the mouth and ears, leaving a slot to shove the RPi4 into the back of the skull.

If you create a case for a RPi4, you can use this scad file to carve the IO holes, or you could subtract the RPi4board-withIO.stl or simpler RPi4board_shaped_hole.stl from your case. I subtracted the RPi4board_shaped_hole from the block and the sphere in OpenSCAD to make space for a Pi4.

Or you could just render the RPi in your case to check for fit and interference with code like: