You might have some success with funeral home records-- the Watts funeral home in Madill or the funeral home in Marietta--you could try for a volunteer lookup in both Marshall and Love counties. Some were taken to hospitals in Durant, Tishomingo, Ardmore, etc. in nearby counties. Consider the location, some people passed away south of Red River in Sherman or Cooke counties, Texas, then were buried in Oklahoma. Some died in the University Hospital at Oklahoma City or a state hospital--Norman, Vinita, Fort Supply, or the TB hospital at Clinton, then buried in their home counties.
For Oklahoma death certificates, I have some in the 1940's with 'can not find' letters, but some were available in 1915-1917-1918 from some counties, depends on the counties.