The 7.5 NAD's system file and the normal 7.5 system file are different animals entirely in the resource fork. I didn't even look at the data fork. If you can trim a normal system down enough, that could be the best solution, but it seems like a long shot to start swapping resources around from floppy to full system. This is why, if it comes to this, I suggest starting from a 7.5.3 disk tools disk and make changes based on the differences between the system 7.5 disk tools and NAD systems. It would not especially surprise me if you could just use the Finder from the 7.5 NAD with your modded 7.5.3 disk tools system file.
I'm not sure if these disks are bootable from a RAM disk - I don't recall ever trying. They certainly won't boot from a hard drive. That could make development tricky. If you have to develop on floppies, you might get away with swapping in a very small application, renamed "Finder" with the Finder to save space. It should then boot and launch that program. with no Finder necessary.
Another possibility that I have never tried is to put the System 7.5.3 NAD-in-development system folder on an HD 20 (non-SCSI) and boot from it on a Mac Plus. The HD 20 may appear to be a floppy drive to the 7.5.3 disk tools system, and 7.5.3 happens to be the newest OS that will boot on that setup.