Both the internal floppy drive and the external floppy drive have an interface board between them and the main board.
The internal and external boards have very similar component sets, except the internal board seems to lack the GAL.
It is conceivable that Outbound used the floppy interface as their expansion bus. I wouldn't want to guess how likely or unlike that is....
Actually, it seems kind of unlikely, because the internal hard drive is bare to the motherboard. Connected with just a dumb cable.
1) Are the internal drive interface and the external expansion bus the same set of signals? Probably not. It looks like the internal interface must be 16 bits wide with 44 pins? Don't have one in front of me, but here's a pinout for the Conner CP2064:
https://stason.org/TULARC/pc/hard-drives-hdd/conner/CP-2064-64MB-2-5-SSL-IDE-AT.html
External interface is almost certainly 8 bits wide, because SCSI chip in SCSI adapter and 85C30 chip in Floppy adapter are set up to receive 8 bit data. I don't think there are bus latches/switches bringing in 16 bits and slinging them twice as fast, but 8 bits at a time to those chips.
It's also possible that the internal interface changes depending on what is detected there...
2) Are either of them the same or similar to the Apple floppy interface. Was that on a 19 pin connector?