So... what's the goal here? A 512k-no-e can't run System 7 so you'd never actually run into that situation. (A 512ke can't run it either unless you use a 3rd party memory board, for that matter; it simply will not run with less than 1MB of RAM.) Do you want to add the Plus ROMs so you can upgrade the internal drive to 800k and/or dispense with the need to pre-boot with the HD20 Init floppy but still otherwise limit yourself to what a real non-E 512k can run? In that case you're not running anything higher than System 5 anyway so the change should be mostly invisible.