Update - October 30, 2016 Good news! Got the new (used) Motherboard, CPU, RAM & case about 3 hours ago.
Everything looks good with the exception of a case fan that appears to be DOA. Luckily, I have a couple of good case fans to replace it with.
The MB and everything else was already mounted in the case, but I had to pull the MB out because whoever installed it missed a couple of mounting point screws. I installed some new brass mounts for it and re-installed the MB back into the case.
I have also pulled the RAM which turned out to only be 2 X 1GB modules of OCZ PC2 6400 Gold. They will be listed on Craigslist as soon as I can get around to it.
Also pulled the CPU, (Core2 Duo 6400 - 2.13 GHz) and Cooler, and replaced with my Q6800 Quad Core and cooler.
I pulled the front panel off of the case and there is room there for 2 case fans, but they are not 80 or 120mm - looks like maybe 90mm, but I haven't measured it. I've got boxes full of fans, but nothing in that size.
I'm just taking a bit of a break now before I pull the Antec 650 Watt PSU out of the old case and move it into the new one. Then, I guess I'll have to pull a DVD player out of my operational computer and install it into the new case. After that, assuming it fires up, I should be set to install a new system onto the WD500 HD (already installed).
I'll post some photos soon...
More good news... Just powered it up. Fans spin, video works, boots up. I haven't plugged in a keyboard or mouse yet, and there is no system on the HD.
Just found an SATA LG DVD burner, and will hook that up in the next few minutes and then install System 7 on the HD...