I was curious as to how long Edwin and Emalyn Keath owned the West Main Street house before they sold it to my parents in November 1957.

I knew from the 1950 census that that house was inhabited by a couple named Clarence and Sadie Miller, so when did they sell it?

As it turned out, they sold it to the Keaths in May of 1957. From the May 28, 1957, edition of the Lebanon Daily News:

So they bought it for $6500 in May and then in November of the same year sold it to my parents for $7200.

Interesting.