I have used OS2 on an A2000/A2091/A2630 for years, you only need to change the KS ROM to 2, I currently use KS3.1 and have changed the ROMS on the A2091 to version 7 (kindly supplied by TjLaZer). but 6.6 work fine with WB2.04.
I think the only difference between WB2.04 & 2.05 is the PCMCIA slot and IDE support that was included on the A600.