Thanks for the ongoing research, I am more inclined to think that it is more likely the mystery car than the Billington car. These images are from a video on YouTube ( www.youtube.com/watch?v=KDOV6MjSOXM ) of Austins Rd hillclimb which even though the video says 59/60 only ran at Austins Rd 1961,63,64,65 according to records of Au/NZ hillclimb events. I also have footage that includes this car that says Puhipuhi early 1960s, worse quality but same wheels and white on the bonnet. This is clearly the mystery car because of the small white bonnet scoop and the painted nose as per the better photo.
My rear end when purchased
here is also a photo of the rear suspension when I picked it up, obviously like everything else it has a coat of red oxide paint no doubt to protect it at some point..
I am currently away from home but hope to pull out some stored items so I can get access to the car when I get home and look for finer details.