I don't have any specific info from La Salle Parish, but I have information on the people you are looking for.
My mother's mother was Emma McDowell Butler, sister to Chester, Fred, Dewey and Jesse, daughter of Issac Henry and Eliza Easley McDowell. In her second marriage Emma married Lynnwood Sloan Butler in Columbia, Caldwell Parish, LA around 1940 and had two daughters, Joy Lynn and Rose Marie. Joy Lynn Butler married Ivan C Greene Jr in Columbia, LA in 1961 and had two children, myself and my brother.
I have specific information on Emma's family (from Hot Springs, AR) but I will have to locate it. My mother, Joy, has many family photos of her McDowell uncles that I'm sure would interest you. She also has a (guestbook?) record from Issac Henry McDowell's funeral, that was written by her mother, Emma.
I have been attempting to research the family further but have been only marginally successful. Perhaps we could share notes?