As far as I know, all you'd need would be a patched kickstart with scsi.device code from the 3.0 one... I don't know if it would fit in the 256kb footprint of the 1.3 ROM, though. If you find a way, please let me know! :-) I'd love to do this, as well.
The scsi.device for the A600/1200 won't run under OS1.3. There's nothing to stop anyone writing one that would, but funnily enough nobody seems bothered
It wouldn't need to be patched into the ROM, a simple device + mountlist would suffice though you'd lose HD booting.
