With those older generation cards, some care is needed depending upon the OS being run. If you're using Linux you should be fine.
If you're running some other OS though (eg ESXi) then they might have dropped out of the "supported list" for the OS and not have their drivers included.
It's amazing what you can do with some sheet metal and tin snips when there's a strong enough need for the bracket to fit a particular slot height. Homelab environment obviously. :)
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Oh, if you have even a hobby grade CNC machine around, you can get a fairly professional level result:
They're widely used (with many different types) in IT data centres, home labs, and probably other places too.
Heaps of them are on Ebay. As a random search just now for "Mellanox 25GbE" on US Ebay:
* https://www.ebay.com/itm/134435757546
* https://www.ebay.com/itm/355348422765
(there are hundreds of individual results)
Searching for "Mellanox 50GbE":
* https://www.ebay.com/itm/225021493021
* https://www.ebay.com/itm/233915360659
(less results)
There are older generation ones too, doing 40GbE:
* https://www.ebay.com/itm/305046322527
* https://www.ebay.com/itm/166350081025
(hundreds of results again)
With those older generation cards, some care is needed depending upon the OS being run. If you're using Linux you should be fine.
If you're running some other OS though (eg ESXi) then they might have dropped out of the "supported list" for the OS and not have their drivers included.