Convert PowerMac G5 to support ATX mobo and PSU

So I recently acquired two PowerMac G5 chassis' that are in okay condition. One has all of the innards and a side panel while the other has the whole shell and some of the innards. All of the boards and fans have been gutted other than the cables and there are a few small dents and a lot of scratches. Can you guys give me some pointers on the best way to sand, paint, remove the dents, and then convert the whole chassis to support an ATX motherboard and power supply as well as a 240mm radiator? I plan to make this a lengthy process to make sure that everything comes out right. I'd post pics of the conditions of the cases but they are currently sitting in my trunk. Any help would be greatly appreciated on what materials I need, estimated costs in USD, and where to get the mobo tray from Lian Li.

There are plenty of people out there who have done the conversion, with varying degrees of aesthetic finish.

This blogger has done one pretty well, keeping most of the internals fairly stock with the original heat segregation.

There are companies out there who have started selling conversion kits... for example thelaserhive.

Dents and scratches.... I would just stick to doing it how it is done with auto-mobiles. You won't keep the original finish in any of these cases as you could just use car body filler to smooth out the dents you can not push out.

As for a 240mm rad, up front and make a bracket out of sheet metal.

My personal advice, would be to find a case of similar size and cannibalise it for the motherboard tray and rear IO plate. Then essentially transplant it so it is Mac outside, other case inside.