Hello Christo.

I believe this is a bitsa.

The 'streamliner' cowling was reserved for more expensive models.
The utes had the rear, top-mounted fuel tanks in the 1960s.
Also, the carby is on the wrong side. The Carby should be on the
same side as the height adjustment lever.

Similar to this (but without Chieftain):-
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=71011

Hope this helps.
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Jack