Hello Jon,
First of all, the system enablers. These were used whenever a machine was released after the introduction of System 7.1. The specific system enabler (see the list above) had to be present in the system folder, otherwise the computer would not boot/function correctly.
As mentioned earlier, no system enabler is needed for System 7.5.3 (nor is it for the Network Access Disk 7.5) in a PowerBook 180c.
You can use one of the other old Macs in order to modify startup floppies.
I would suggest that you create three Network Access floppy disks (see above) to begin with. You can use Disk Copy 6.3.3, but ensure that a properly sector-copied disk is made from the disk image via the Make a Floppy command. Do not drag-copy from a mounted image. Often, Disk Copy 4.2 (the Make A Copy button) is easier to use (only for Disk Copy 4.2 type images, such as for the Network Access Disk).
Then, download, decode and decompress Apple HD SC Setup 7.3.5 (link above). Open a Network Access floppy. Remove everything from the three folders Apple Menu Items, Control Panels and Extensions (inside the System Folder of the floppy). Empty the Wastebasket/Trash. Copy the HD SC Setup program to the base level of the floppy.
Next, download and decode Drive Setup 1.7.3 (link above). Mount the .smi (double-click on it). Drag-copy the mounted "disk" to the hard disk of the machine that you are working with. Creating free space as above is not going to be sufficient here, so another method is used. Open a new Network Access floppy. Open the System Folder of this Network Access disk. Move the System suitcase out of the System Folder (to the floppy's base level). Move the remaining System Folder to the Wastebasket/Trash. Empty the Wastebasket/Trash. The System suitcase would at this point be the only file in the Network Access window. Drag-copy the Drive Setup application to the floppy. Rename Drive Setup; call it Finder instead.
Finally, if a suitable third-party SCSI formatting utility can be located, you may want to use a method similar to the one for Drive Setup 1.7.3 for yet another bootable tools disk.
Jan