1972 700 series
This is a 1972 700 series. Sears catalogs refer to them as 700s not 70s for some reason. This one is the introductory issue of this model since it's model number ends in 700. Later revised models ended in '701, 703, etc.
One of the revisions to the machine indeed was the plastic tub ring, which was added in early 1973.
There was a flirtation with plastic outer tubs at about this time. I am not sure how many models this encompassed, but every one I have ever seen (like three machines total) was in the same 1973 KM 60-series plastic control panel model.
This model for sale is a very nice machine. There isn't much missing in the way of features that would be needed on a daily basis, but there were two models above this machine, the 800 and the garage door Lady K 900 for those wanting even more.
Gordon