I compared the System 7.5 Disk Tools to the System 7.5 Network Access. The network access system file is the same as the disk tools system file, with several extra resources:

'AINI' (all)

'atlk' (all)

'drvr' (all)

'DRVR' 9, 10, 40, 126, 127

'ecf2' (all)

'ecfg' (all)

'enet' (all)

'ICN#' -16411, -3978, -3977

'ics#' -3980, -3978, -3977

'iopc' (all)

'lmgr' (all)

'ltlk' (all)

'STR ' -8192

'STR#' -16503, -16411

and then both 'VERS' resources are modified to reflect the version.

These extra resources are NOT the same as the ones in the full System 7.5 system file. I would recommend adding these resources directly from the 7.5 Network Access disk to the system file of the 7.5.3 Disk Tools disk and see what happens. There are several revisions of 7.5.3 disk tools disks, so I'm not sure if all of them are Power Mac bootable. It seems like they have different size System files too, so you could try a few of them to find the smallest one that's bootable. It might still be too big after this, but you could probably find some other things you can chip away to make room too.

If this is more than a curiosity, a quick option is to just use a CD-ROM or external hard drive with the full System 7.5.3 installed. That's nowhere near as cool though.

There are some techniques out there to write beyond the capacity of a floppy disk, I'm not sure if that works on Macs or not but Microsoft was known to do this with Windows installer floppies. It saved disks and made them hard to copy - that was awesome for them.