If you need a bracket, I do have a spare single bracket that'll fit in the spot. Came out of one of my parts machines a while back. With respect to the OS, if you can get an 800MHz or faster G4 chip, it'll run 10.5.8 perfectly fine with no hacks. Got a 1.2GHz G4 chip in my DA and 10.5.8 installed just fine on one of my drives. Otherwise, 10.4.11 is what you'll want. That's also the last version that could do Classic, from what I've read.

-J