Apple PowerBook (Duo 270C) - Manual (Page 248)

8. Turn the subassembly over and put it down with the
disk drive(s) facing up.
v About NuBus slots and cards: The two NuBus slots in the Duo
Dock are stacked vertically. The slots are identical, so you can
install your card in either one. If you install your card in the
upper slot (which is the lower slot when the dock is right side
up), you’ll have to remove it and reinstall it if you want to add
a second card later.
NuBus cards come in different shapes and sizes. All properly
designed cards will fit into the Duo Dock. You may find it
easier to install a large card in the upper slot rather than the
lower one.
v
9. Remove the plastic NuBus card guide next to the floppy
disk drive by pulling it straight out.
NuBus card guide
Hard disk drive
Floppy disk drive
232 Chapter 13: Building a PowerBook Duo System