Hi Red Rum,

Going by the link below as you mentioned the other AV having a Clinton motor has the A on the id plate ,you would assume the
A represents a Clinton 4 stroke motor but only seeing a couple of mowers with the A and a Clinton it's just a guess.

https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/106808/austral-villiers-hercules-c1959.html

It's up to you how you would like to restore this mower base ,the Clinton 4 stroke is harder to find than the Kirby but
all 3 four stroke motors will bolt straight on as the pattern is the same even a briggs will bolt straight on.

Pics below showing bolt pattern the same for Briggs and Clinton 2 stroke and is the original Kirby pattern.

Cheers
Max.

Attachments
Briggs 2.jpg (109.63 KB, 45 downloads)
Briggs 1.jpg (73.81 KB, 45 downloads)
Clinton 1.jpg (86.01 KB, 45 downloads)