Here is what I have on Francis Marion Caywood. He was born Oct 1837 in Hendricks County, Indiana the son of Horatio Caywood and Zillah Caywood. The family lived in Tipton County, IN in 1850 and moved to Harrison County, Iowa in 1852. Francis married Elizabeth Perry (Petty) on 21 Mar 1858 in Harrison County, but he was living with his parents in 1860. I do not know if Elizabeth died or they divorced. He married Mary Blunt on 18 Feb 1862 in Harrison County. Mary died 2 Oct 1867 and is buried in Magnolia Cemetery, Harrison County. She is listed as 25 years old and the wife of F.M. Francis married Mary E. Williams on 3 Oct 1869 in Harrison County. They had at least 8 children and were divorced between 1895 and 1900. He was living in Harrison County, Iowa in 1900. Francis served as a private in Co B 13th Iowa Infantry during Civil War from Nov 1864 to Jul 1865.
On the 1870 census Francis is living in Harrison County with wife Mary age 28 and son? Mancy age 7. There is also a Erin Cole, male, age 8 living in the household. I believe it is probable that Mancy is actually Nancy, the daughter. The marriage date to Mary Blunt and birth date of your Nancy Asberean Caywood don't quite work out, but it would not be the first time that a birth happened after only 7 months of marriage. On the 1900 census Nancy Caywood Ross listed the birth place of her mother as Ohio, but on the 1910 census she listed it as Missouri. I have briefly tried to track down a connection to any Blunt family in those two states, but with no luck.
I would be glad to send you my .ged file with Caywood data and anything else you might desire. I have very extensive census record extracts in pdf form.