I received an old AM3+ motherboard and processor with its backplate and retention brackets missing. The latter I could find here.

Sadly I found no suitable backplate so I whipped out Fusion and made one.

I recommend you to print with something more temperature tolerant. I chose PETG for mine.

It still has a problem with it bending the motherboard under tension from the cooler but I read it is not that much of a problem.

Feel free to improve on the design and its rigidity.