i have a wild theory and I'm going to throw it out here for "just in case."
In 1880, James H. Clark and his wife Kate Williams Clark were living in Clark(e), Lincoln Co., Missouri. In the household was James's father, William.
Also in the household, but not indexed together on Ancestry, was a farm hand, M.H. Young age 46 (abt 1834) MO. both parents born KY.
My theory is that M.H. was Matthew Young, b. 16 Feb 1834 probably in Ripley Co. MO, son of John K. Young (b. abt 1808 KY) and Nancy Clark Young. I further theorize that William Clark was a brother of Nancy Clark Young who was married to John K. in 1832. That would make William Matthew's uncle and James his cousin. I have scant info on Matthew other than the name and birthdate. He can be found in Ripley Co. in 1850 in the household of John K. Young. Nancy died in 1840 either in childbirth or shortly after. That baby died at 9 days old. John K. remarried in 1841 to another Nancy who died in 1850. John K. died in 1855. John K. had 3 sons by Nancy Clark and 2 daughters and a son by Nancy Stalcup. I've been searching for the older boys for 25 years. They were not in Ripley Co. in 1860 and apparently either scattered to the wind or they all died.
The only catch in my theory is the birthplace of Nancy Clark Young. I don't know her birthdate or birthplace. The 1880 census states that William was born in NC but the Clark family could have moved from NC to KY before settling in MO.
Thanks for your indulgence.