Hi Paul

I would say that was very good detective work there.
The 853A specification did go to a Qualcast 16" Sidewheel Powermower.

Here's the confirmation here:

[Linked Image]

I did write a History Record for these mowers, filed under
Australian Power Reel Mowers (because they were made here)
It would appear that the engine was fully imported (lacking the X number).

https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=60359

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