The iUniker case on Amazon is a great little RPi 4 case, cheap and works well. But I didn't love the small fan, especially since there is plenty of room for a 50mm.
Parts:
This model requires no supports and the pegs are purposely spaced a little in for a friction fit. It sits on top of the case making it slightly taller to allow for airflow around the larger fan.
If you want to modify it, you can find the design on TinkerCAD: https://www.tinkercad.com/things/9hOL77ztKEk
I will probably add a version with a fan guard of some sort, but I don't want to add noise or reduce cooling.
I'd also suggest using the 3.3v pin so that it runs a bit slower.
The author marked this model as their own original creation.