Someone gave me a machine
I found the Instruction Manual for the 6000 Series machines (6010 and 6020) on www.sewusa.com available for purchase: $15 including shipping.
Additionally, the site says they will post a FREE Threading Diagram for any machine for which they have the manual. You need only make the request through their email link on that site. They already have posted Threading Diagrams for several Viking machines, however the 6020 is not yet posted. I emailed a request tonight. Hopefully they will get it posted soon.
Let me know if there's anything more I can do to help.