Its not necessary that the boot partition for OS4 is an old FFS partition.
(sorry, I know you know this, I just write this as general information )
It better not be, because AmigaOS 4 needs to be installed on a partition with long filename support.
The distribution CD contains 68k versions of SmartFileSystem and FastFileSystem that can be installed on the RigidDiskBlock so that the DOS/7 disks can boot under Kickstart 2.x/3.x as well.
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