What I was thinking was to open a network access system file, and the same version of a normal system file, and compare them in ResEdit to see which resources are completely missing. For example, all color icon resources are probably missing on the network access one. So then you could try removing those same resources from a System 7.5.3 system. This could be any type of resource, not just icons.

ResCompare is going to actually look inside of resources, and that's not what you want. You do want the differences that 7.5.3 brought to the system file to remain in there.