Hi Justin
I see you've found
my C15 page!
The basic difference is the first one is a Canadian designed and built body; the second is an Australian designed body built by General Motors-Holden.
When posting images, it's good form to credit (and link to) pics from other sites when you post them
This is from my
C15A page and shows a number 2 Australian body with valances over the wheel arch.
This image from the same page shows the earlier version without the valances.
The canvas roof on these pages is unique to Australian built trucks and is called the "Sunshine roof".