Hey I'm new to all this! Plus it was late and most of my thinking faculties had gone to bed for the night. I did look at the pinout but I was mainly concentrating on the +5vSB pin. Anyway it all worked out good in the end, thankfully.
I've bunched up three of the sets of cables coming from the PSU, tied them and wedged them in behind the fan bracket to keep them out of the way. Whoever took out the hard drives also took the hard drive caddy for the IDE drive. So I used the middle hard drive carrier and placed some little dampeners between the carrier and the drive to help with any vibration. I dug out the horrible, horrible pair of "pc speakers" I got with my first PC. Should do the trick for hearing sound out of the line out for now.
So now I finally have my first G4. A whole new world of Altivec awesomeness unfolds.
OK, with the speakers plugged in I hear a faint chime, so there must be something up with the internal speaker. Something to look into later...