Agreed the 1700kg weight does seem overly high for it.
The Lips you’ve posted for comparison is externally very similar indeed, in fact I’m more convinced on the mystery safe after seeing that, there are way too many similarities for it to be anything else.
As you know Lips were a highly respected maker and were the number one choice for heavy banking equipment in many European countries. Perhaps that particular safe is also one of a few ‘specials’ they made for a particular bank or customer like Chatwood did for some of theirs.
BTW I have re-titled the thread in the hope it draws more views and interest from searches, hopefully someone out there will recognise it.