What Candace said. There is great information at the "Vikingsewingmachinespre1980" Yahoo group.
I've had 2 of the 6000-series Viking machines, a 6440 for free and a 6020 for $5. Both had a cracked cam and needed overhaul. Fortunately, I found a great Viking tech about an hour from me and paid $189 +parts for each machine. The 6440 was complete, but the 6020 only came with the foot controller, one pressure foot, the A cam, and the manual. I was lucky to find a set of attachments in the tray at an estate sale for $3.
Great workhorse machines. The only ones I know of that have a low gear (pull out the bobbin winder to engage). My SIL has the 6440 now and I kept the 6020 because it was the last TOL in the series that was not self-oiling. It's designated for my Hubby's use, he is a Black Powder reinactor and makes his own gear.