Ken:
Back at the time this range was made, Sears operated somewhat like Walmart does today - they laid down specifications and a price point, and told manufacturers that they would either make the product to those specifications, or not get Sears' business.
This was the way that Sears offered such great value at that time. A case in point would be Sears' Lady Kenmore washer of 1966 and the competing Maytag A906. The A906 carried a list price of about $429.95. The Lady K's catalog price (exclusive of freight charges) was $239.95 - and the Lady K had more style, more glamour and more flexibility than the A906.
There was a downside. Sears had very little supplier loyalty; whoever was willing to jig to their tune got their business - until someone else was willing to work for Sears cheaper. They were also notorious for not accepting responsibility for their mistakes; if a merchandise item they designed did not sell according to expectations, Sears would cancel orders no matter what. This practice almost put a clothing company my grandfather worked for out of business; a coat produced there didn't sell, and Sears canceled, saying in effect, "sue us," knowing very few companies could afford to take Sears on.
The company my grandfather was with survived, and eventually Sears came around again, dangling an attractive order. But this time, the company's answer was, "Not only no, but Hell no."
Sears did buy into some companies like Whirlpool and Roper, to get additional leverage. I think Whirlpool probably would not be around today if it had not been for Sears and their huge buying power.