According to Wikipedia it is an Intel 820 chipset.

My chipset knowledge is mostly from this era. Don't ask me about anything contemporary. My head is cluttered with lots of obsolete computer hardware trivia. 😊

The only time I used ducting is when I had a large fanless heatsink for a CPU and a large slow undervolted case fan. It worked quite well. I did it in order to make the machine as quiet as possible. If your current setup is working without issue I wouldn't bother with ducting unless you are in the mood to tinker. I'm guessing the case is somewhat cramped so that might make it a bit more challenging.

Okay, after running the 'Stress CPU' in CPU-Z for a while and watching temps in SpeedFan, I have no idea where it's got temp sensors. One is near (or in) the CPU, another is somewhere on the motherboard, and the HD reports temp. So the Noctua fan is working wonderfully; the heatsink is cool to the touch even after a couple hours of the stress testing.

Now I need to figure out how to fasten one or two of those tiny 1U fans in the HD cage, and/or optimize airflow and all the IDE cabling in there. Maybe some basic foam filters...? Was terribly dusty inside when I found it; went through two full cans of compressed air, and there are still a few dust bunnies hiding in there......

So I think I am finished with this little project for now. Other than finding an EB CPU and repasting it. I don't really have a use for the machine at this point, so I think I'll close it up and put it aside.

As for the small fan I pointed at the GPU, that's mounted and ducted. I'm actually pretty proud how well it worked out.

All been added to album link in the OP, but here it is anyway!

https://imgur.com/a/f1mRj

Added some descriptions, CPU-Z screens, couple fancy shots.