FreeBSD 4.8: can't load kernel after doing "cp -R /" to another disk

[admin at azuni.net]

>> 
>> Hello, everyone. This is the problem: our SCSI disk with FreeBSD 4.8
>> on it has been failing recently, so I copied its root partition to a
>> fresh IDE disk with cp -pR and 
> 
> You should use dump and restore to copy the root partition, see:
> 
I'd done that before trying cp -pR, as outlined by rse@:

dump -L -0 -f- /old | (cd /new && restore -r -v -f-)
http://people.freebsd.org/~rse/mirror/

which isn't too different. I think I know what the problem is: I made 
the new single slice and FreeBSD partition on it and ran newfs -U on it 
using the latest FreeBSD 5.x livecd toolkit, and later 4.8 can't even 
mount that partition (mount /dev/ad0s1a /mnt) failing with "incorrect 
superblock", so I think its /boot/loader can't load the kernel because 
of FS issues (but strangely enough pressing "?" at the boot loader 
prompt lists directory entries of the root FS just fine). It turns out 
UFS isn't upwards compatible from releases 4.8 -> 5.5. I'll try running 
newfs -U from 4.8. Last time I checked many 4.8 binaries couldn't run 
due to disk errors, I hope newfs runs ok...