I looked for Robert & Missouri on GA Death Index. I found Robert F Burtz d 3 Oct 1927 in Cobb county #23773-I Perhaps this is your Robert C Burtz, I don't know if the date matches the tombstone or not since I only wrote down the years.I have found conflicting information of names on GA Death Index.I didn't find Missouri on the death index.I tried various spellings for Burtz 1936. I also tried Missouri, but nothing matched.She may be recorded by a middle name, or I may have copied down the incorrect year of death.
I checked the LDS 1880 census--all US, all variations of spelling Burtz, all Burtz white males b + or _ 1859 and found nothing that fit.Furthermore he's not a descendant of Lebbeus W, James Barret, or Levi F Burtz as those are the Burtz lines I'm looking at closely.
You probably need to find him in 1920 census and work back from there.