Unfortunately, there was not enough space to use one of the Mac's dual fan arrays since the fans were larger than the PC's, so I saved myself a lot of effort by instead using that space for the PSU, adding a reversible bracket to the inside and a second back plate to the outside (5 separate layers of metal at its thickest point). The order of the metal sheets was: Donor motherboard IO panel (Inside case) > Mac rear panel > Donor PC rear panel. The rear frame of the donor PC served as a back plate to sandwich it all together once re-riveted together. The rear IO consisted of several layers, but the smaller one could be removed from the back panel once the rivets were drilled out, allowing it to be used as a template to cut out the back of the Mac. I worked out the positions to drill the holes on the donor motherboard tray by painting the tips of the Mac's standoffs white, placing the tray on top, pressing down, and drilling out the centre. The rear IO panel, motherboard tray and PSU bracket had to be cut out with an angle grinder.

The most common motherboard standoff mounting seemed to be JB welding the standoffs to the inner wall of the case, but I actually used the existing standoffs to mount the entire motherboard tray from the donor PC onto. Other Mac G5 conversions have used methods like mounting an ATX PSU in the existing power supply and removing the upper partition to have a higher motherboard, or fitting it in the top where the HDD cage is.

The trickiest part of the build was making it compatible with ATX motherboards and PSUs.

Power mac g5 case mods