You may try to use NetBSD to mount those disks. In
the days of
NetBSD 1.4 I mounted a SunOS 4 drive from NetBSD/sparc without any
trouble. NetBSD uses the same disklabel(5) layout as Sun and the
file system is AFAIK just the same.
In the 1.4 days these were within epsilon of true. They are less so
now (NetBSD now keeps a BSD label on the disk, with the Sun label kept
around just for PROM bootcode compatability, and NetBSD ffs has evolved
significantly beyond the SunOS 4.x filesystem), but I think that even
NetBSD-current can grok Sun-labeled disks and UFS filesystems.
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