I now think the J. M. Garst in Gage Co. NE was John M. Garst, son of George B. Garst and Katherine Markey from Botetourt VA. John M. Garst's son, George Washington Garst and wife Sarah Ann Gibson were definitely in Gage ca. 1880. They buried a child there,in the Brethren Cem: Charles, age 2, in April 1881. I have not found anyone who can verify that J.M. in Gage was John M., but I'm fairly certain he was. Moreover, James Marion Garst from GA was never a famer--he was a phrenologist! But if anyone is looking for John M. in 1886-87, try Gage Co. NE!
We have not been able to place James Marion Garst's children by Fannie Houseworth in NE, but we have identified them in the 1880 census in Fulton Co. GA: J. M. Garst, wife Fannie Garst (Houseworth), children James E. Garst, born GA 1871, and Fannie Garst, born GA Apr 1876--along with John A. Houseworth and his sister, Mary E. Houseworth--both listed as Garsts in the 1880 census. James E. Garst and Fannie Garst Jr. both died in Fulton Co. GA in 1951. Still working on son Charley Johnson Garst who was born after the 1880 census.