G'day John
My interpretation of the numbers makes this a 1974 Imperial.
The 2-strokes were introduced in 1972.

This is a 16" in what appears to be good condition.

I have written about them here:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=72729

A good, solid design based on the British Ransomes MK7 design.

Parts: depends what you want.
Generic wearing parts may still be sourced. Bearings from a good bearing supplier.
Other bits may require ingenuity ... and tenacity.

Many thanks for the great image record!

Cheers
----------------------
Jack