[Arran]

 Putting a battery set that has been converted to AC in that fashion back to battery would probably be easier then trying to make it work as is, but you would have to make an inventory of what original parts are still in place and get rid of anything that isn't.  However if the chassis that the Radio Corporation of New Zealand built are identical to the Pacific radio ones other then the data plates, and dials, and are relatively easy to find, I know what I would do. 
 As always seems to be the case with farm/battery sets converted over to using AC tubes it's usually a hack job, and you really have no idea what they did, who did the work, or even whether it worked afterward. The smart ones kept the original tubes and circuitry as is and built or purchased a battery eliminator to operate the set on AC . The stupid ones do things like what was done to this Pacific, and I think that the quality of their work shows that they were really in over their head, this was not carried out by a service shop this was done by someone as a weekend project.
Regards
Arran