From what I gather, network access disks squish everything in there by removing some system resources. You could theoretically compare an existing network access disk's system file's resources to its full-version counterpart and remove the same resources from a 7.5.3 system file. Realistically, this probably won't squish it down enough in size and/or will break it for some things you'd like to remove. You may get away with using a pre-7.5.3 Finder. If not, you'll probably have to do the same thing to the Finder.

It's not a complicated thing to try, it's just time consuming. You would have to make a backup whenever you have a System File that still works, and test after every few things you remove.

This is the sort of thing that could even be attempted in SheepShaver. Undoubtedly there is some FAT code in the System File that could be stripped of its 68k code - that could in fact be complicated and tough to test.