Hi Alex That's an amazing piece of detective work.
NZ's Challenge Corp. - who owned Morrison at the time - also owned Scott Bonnar. The 690 was a Morrison design and fully imported (I think).
I was not aware they moved to a plastic bearing housing, but that now seems likely.
The metal housings were designed by Ransomes and used from the Minor MK6 of 1951. In Australia, they were used on Victa Imperials, Scott Bonnars, and Morrison-Turners. You have a good chance of tracking down a metal one on auction sites.
