As far as I know, the upgrades NewerTech and all sell are not compatable with the Network Server 500 or 700 machines.
I believe the CPU cards are compatable with the 9600 machines, so you might be able to put up to a 350MHz Mach 5 CPU in a Network Server 500.
I belive LinuxPPC has some info regarding the Network Servers on it's web site.
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Eliott Wolfe
Winnetka, Calif