Thanks again for your responses. I have been aware of YDL for quite some time (and, indeed, of its sad demise), however I will be using Fedora for PPC (at least 8, if not later). Access to RSX (the only significant limitation imposed by the original OtherOS, if I remember rightly), BD, or even a GUI isn't required; all I'll need is SSH access and full support for the USB.
The delay in the Ethernet response times caused by the GameOS hypervisor won't cause a significant issue either, although Ethernet will still be required. If I can retrieve OtherOS - preferably in its original form - by installing v3.15 or similar then I'll have all I need.
Is there an upper limit to the PS3 firmware version that I'm going to be able to recover OtherOS functionality from? There seems to be a difference of opinion as to whether the most recent version that can be downgraded is 3.55 or as recent as 4.x.
My aim is to downgrade each machine with as little effort as possible. By-the-by, if I get it working I will be offering good - but not excessive - money for PS3 fats with broken BDs and the like.
Again, thanks very much for your replies!