Each revision is slightly different - so that is one for the single 1.6, one for the
1.8, 2.0, Dual 1.8, dual...... ( you get the picture ! ) Then theres PCI & PCI-X
versions, Then you have fan / air cooled or water-cooled
So the chances
of finding EXACTLY the right one are slim.
Buy another G5 & sell your dead
one without the HD - its usually cheaper and quicker.