All of the 4000s I've seen have had standard-sized HD drives and a normal bay free.
Most of the early ones sold in European countries had the A2000 style 1,5 height mechanism. I've personally seen more of those than the 1" high ones.
Macs had roms that were patched by the upgraded os at boot. pulling the roms and replacing them is only needed to run os versions newer than are supported, and is pointless. os 8.1 on an se/30 anyone?
The AmigaOS also patches the ROMs at boot. Setpatch. Of course not quite the same, as you can't have a higher major version of workbench than is your kickstart..
