Here is a pic of the bracket described above, made from two case expansion port covers. It secures an ArcadeVGA card.
Card is bolted to the bracket at top. You can just see the "foot", with two screws securing it, below the USB cable. The bracket needs to come out to one side obviously, otherwise it will block your ports. The bolt you see in the middle/high holds the bracket together (not attached to the card itself), there's another one at middle-low, hidden behind various cable heads. It is quite secure, despite that heavy video cable hanging off it, and even when the cab is moved around significantly.

Made that from whatever was in my junk boxes. The bolts are a little long, just what I had at the time (looooong time ago).
This PC was for a cab, and built into a plywood drawer so it just slides out for servicing, can even remove the whole drawer. Also made brackets to secure the power supply and pulled the hard drive cage out of an old PC case to support the HDD drives (not shown).
Pic is around 15 years old! Sorry can't give you a better pic. Sold the cab to a mate, but recently visited and gave it a thorough service and update, Put in new PC, SSDs, games, music etc. and nice new speakers. Was able to use the old video card bracket with new mainboard & card. It lives again!!
