mounting a 4.x drive under 5.2-BETA

[Aditya]

So I have a second drive in my 5.2-BETA running Netra X1 that I had in a
4-STABLE i386 box that I mounted as:

  /dev/ad2c            /data           ufs     rw              0       3

I get a complaint when I tried to mount it. Since mount doesn't have any
special options for mounting a UFS1 partition, I can't figure out what I might
be doing wrong...

Am I trying something that is impossible?

some# mount /dev/ad1c /mnt
mount: /dev/ad1c on /mnt: incorrect super block
some# uname -a
FreeBSD some.lan.grot.org 5.2-BETA FreeBSD 5.2-BETA #0: Wed Nov 26 23:53:05
GMT 2003     root at luthien.local:/usr/obj/usr/src/sys/GENERIC  sparc64
some# bsdlabel -A -m i386 ad1
# /dev/ad1:
type: unknown
disk: trunk
label: 
flags:
bytes/sector: 512
sectors/track: 63
tracks/cylinder: 16
sectors/cylinder: 1008
cylinders: 155061
sectors/unit: 156301488
rpm: 3600
interleave: 1
trackskew: 0
cylinderskew: 0
headswitch: 0           # milliseconds
track-to-track seek: 0  # milliseconds
drivedata: 0 

8 partitions:
#        size   offset    fstype   [fsize bsize bps/cpg]
  c: 156301488 0 4.2BSD 2048 16384 89 # "raw" part, don't edit
bsdlabel: partition c is not marked as unused!
bsdlabel: An incorrect partition c may cause problems for standard system
utilities

Thanks,
Adi