Nice work, I'm focusing my efforts on collecting the same "casings" of Powerbooks (ie. based on shape, not model). My wardrobe would not cope with desktops. And I'm almost there! I'm receiving an "untested" PB 1400cs/166 sometime this week, and going to pickup a 1400c screen for it, if it's functional.
Your PB500 PPC story reminds me of my own - I picked up an "untested" model for $19.95 sold by Simply Sold, a third-party company in Australia that sells on items for commission (the shop didn't last long). Had to pay $5 to pick it up, one of their stupid rules - but was pleasantly surprised to find it was a PB500 with Newertech PPC 167Mhz, 40MB RAM, 500MB HD (sadly not the SCSI --> IDE version, but I can't complain!). I also picked up a Rev C card cage off here some time ago for it - let me know if you want the model number.
JB