Check out
http://www.patternreview.com for reviews of these machines. You may have to join (it's free) to look at the older reviews -- well worth the trouble, IMO. Here is a link to one thread I found there quickly; I'm sure there are others.
http://sewing.patternreview.com/cgi-...ard.pl?t=20409
You can also get a lot of information from a group on Yahoo. Here is a link to their home page:
http://groups.yahoo.com/group/viking...chinespre1980/
This won't do you any good for a purchase decision tomorrow but, if you do decide to get the machines, it is a great group for finding out more about them, information on how to clean and repair, where to find parts, etc.
I think the older Vikings used cams for embroidery. You should be able to lift a lid to see a cam in place for regular stitches. If so, be sure to ask if the embroidery cams come with the machine; they are often lost when separated from the machine, along with any accessories such as extra feet and bobbins.