According to "Workbench Nostalgia", by Greg Donner,
there is the same 3.1 ROM for 500/600/2000.
For 2.xx, instead, 2.04 was shipped with 500+ and 3000,
while 2.05 was required for 600 exactly for IDE and PCMCIA.
It is interesting that a "rom upgrade kit" which I own (used for a 2000) was shipped with 2.05 Workbench (37.71) but 2.04 kikstart, suggesting that 2.05 roms were only needed for the IDE and PCMCIA of the 600.
regards