Raspberry Pi 4 Modular Stacking Cluster Case Without Walls

I realized the easiest way to make the original case compatible with Raspberry Pi 3 and 4 was by removing the walls. That also increases air circulation.
I used nylon standoffs from https://www.amazon.com/gp/product/B06XKWDSPT. You may prefer metal ones.
Instead of a bottom piece, use short standoffs for 'feet'.