I just started looking at my Calderwood lineage (John Calderwood is my great great grandfather) on my maternal side and I don't have information on your search for John and Jean from Scotland. But it is possible that my great grandmother, Agnes Calderwood, is the daughter of this couple that you indicate moved to Iowa.
My mother thought her grandmother, Agnes, came directly from Scotland as a daughter of John Calderwood. However, her memory is very sketchy at best at 89. If her grandmother is the Agnes Ann Calderwood of the John and Jean of your search, she married Salem Towne in the Iowa/Illinois area in 1880's. Salem and Agnes Towne produced a daughter, Minnie, and three sons, Ward (Dennison Ia), Roy Salem (Bismark ND), and Ray (Sterling Co). My mother Dorothy Jean Towne is a daughter of Ward, a farmer in the Dennison Iowa area.
Does this link into any info that you have, James?