Logic would suggest a common main board be used for both machines to maximise buying in cost efficiency though volume. The board could then be populated with a different set of components for each production line 2400 or 2600. Aside from the difficulty of the differences in tooling of openings in the outer casing, the next problem might be whether the internal bus system to the micro can accept two input routes from floppy and SD like the KN7000, or whether one input is "hard wired" via firmware to only recognise either one or the other. The firmware would certainly need modifying to enable the SD load button to recognise the floppy too and then bring up a floppy menu system. A further problem might be the actual floppy drive since on previous boards these have been proprietary interfaces meaning that a cheap pc floppy drive would not necessarily fit. Sorry to be negative but it does perhaps seem a complicated hardware and software modification.

If you could describe why you need a floppy some workarounds can be suggested. For instance I have always used the supplied 8MB card as a means of quickly transferring many files from pc to SD in card reader with windows explorer using no software at all. Likewise if you want to email a file to someone from SD card or copy to a floppy no software is needed again. You only need software to start tidying up further additions to cards, make larger cards from smaller, renaming etc etc.