there is a dissassembly of the boot rom for the 990/4 up at
www.spies.com/aek/orphan.html now, along with one for the 990/12.
If you have a way to dump the boot proms, it would be interesting
to see how similar they were.
If you have a way to take pictures of the boards, I'd be curious
to see what the I/O cards look like, esp the floppy controller
board.