Hi Johan,
The firing order can be found in the website's "Repair" section, within the
"Electrical" subsection, then either "Plugs and Wires" or "Distributor".
Here's a direct link:
http://www.imperialclub.com/Repair/Electrical/distributor.htm
On that page you'll also find a link to a picture showing how the 413's (and
all Chrysler V-8's) cylinders are numbered, as well as how they connect to
the distributor cap:
http://www.imperialclub.com/Repair/Electrical/PlugWires.JPG
Best Regards,
Mike Trettin
1956 Imperial Sedan, Turquoise