I've made a new design for the Raspberry Pi 5. Basically it's the same as original only to fit raspberry 5. Front wall is thin to allow installation of PoE M.2 HAT, like this.

I prefer print this in PETG for more “springy” clip.

Assembly is easy - you need 

• 2x 3x12 self tapping screws
• 4x M2.5x12 hex screws (I've used button heads)

1. Install the clip with 2 self tapping screws using premade holes
2. Undo the bottom scews of the PoE HAT (I presume you want rack mount with PoE HAT installed)
3. Put board sandwith onto the mount as show on the picture below. 
4. Fix it with M2.5 screws

For the rack itself - follow original design. Works like a charm for me for a long time now.