If you've never taken the G5 CPU outer cover off (the flat vertical panel that has a large G5 or 2 x G5 logos, if it's a double processor/2 CPUs, embossed/highlighted on it), then it can be a bit fiddly/awkward to remove, as there's a plastic rivet that's almost flush with the top of the steel panel above that panel I have described, but it can be teased-out with a sharp robust tool, like a chisel or such-like. The rivet is in 2 parts, a centre slim inner core part that splays the outer rivet into its locked position, so you need to slide the inner part out first, then put a screw of a suitable size in the hole of the centre part of the exposed rivet, and pull the outer part of the rivet out of the housing/plate.

I hope I have described this procedure sufficiently well for you to work out what to do, but if anyone else has anything else to add then by all means ......

Have you got a spare working CPU, as that can be as much of a trouble as anything else in acquiring?

You'll probably have to look around the internet for the ASD v2.58 CDs, unless someone can send/give you a copy of those files.