Zen Cart formats addresses according to established international standards/formats. Hence the display of the address block on invoices is done using the same logic.

If you want to use our own standard regardless of what the postal company's standard address format is, you will need to write custom code to do that.
The Zen Cart code to do it for admin-related content is in /admin/includes/functions/general.php ... in the zen_address_format() function.