In the meantime, have restored the original header.

More ideas are always welcome.
 
Progress has been made!

I was able to "find" my xfs filesystems for / and /home on the new pv, and dd them into a mountable state.
Thanks mostly to: http://www.linuxweblog.com/backup-restore-lvm-dd

So I now have access to /etc/lvm/archive, which contains the lvm config before I executed the last command.

Allegedly I should now be able to restore my system to this state, by doing:

pvcreate -ff --uuid 3mpxNE-c7Ll-sK5G-MPWq-QZd8-oxvh-E0M7ex --restorefile /tmp/archive/system_00034.vg /dev/sdg1

To restore the pv to how it was, then

vgcfgrestore --file /tmp/archive/system_00034.vg system

to restore the vgs

However, the next snag is:

root@ubuntu:/tmp# pvcreate -ff --uuid 3mpxNE-c7Ll-sK5G-MPWq-QZd8-oxvh-E0M7ex --restorefile /tmp/archive/system_00034.vg /dev/sdg1
  Couldn't find device with uuid aMQJEI-DzSA-BzZ8-Kk8G-tOyz-m2n1-VWXTOe.
  Couldn't find device with uuid 3mpxNE-c7Ll-sK5G-MPWq-QZd8-oxvh-E0M7ex.
  Can't open /dev/sdg1 exclusively.  Mounted filesystem?

Can't open /dev/sdg1 exclusively? Why not?
No filesystems are mounted, lsof says nothing is open.
Googling suggests dmraid may have 'stolen' the partition, but I have no idea how to reclaim it.

At least if tonight I need to trash and start from scratch, I have my filesystems to restore to.
cheers,

     / Brett