Nige,
What you've said about the colours of the car appears spot-on. And your description of style 2 is exactly right - there's a small piece of stainless across the width of the C pillar to separate the colours.
The second half of the trim number refers to the
interior colours, and 630 = Viscount Blue & Black.
The switch to style 3 for Melbourne manufactured cars occurred in June 1959, at body no 22271-M. (Second time I've written that today!) There's no way your car could be as late as August, 8000 Melbourne-made FC-225s before the change-over.
More like April, I would think.
cheers
RET