I was going to tell you to go with the reference cooler they put on the GF3 cards but it seems the Aliexpress seller I bought them from a few years ago does not sell them anymore.

To bad as I picked up 3 of these for $4.00 USD each about 3 years back.

I switched to a FSC-S2 and this machine with AGP slot has also thermal/stability problems with passive G550 or FX5200...beside searching for a solution for the GF3 ...I am also thinking about such a thing:
https://www.ebay.de/itm/110998383409? I can't believe that such a thing is not a professional product and therefore not available for buying... strange.

You can buy 2$ PCI bracket from china that will take larger fans and work much better. But then it's not 1 slot cooling solution is it?
download/file.php?id=105979&mode=view

For that FSC-S2 I need the PCI-Cooling Solution in LowProfile (LP).