I will check out the web postings. When you call Oak Grove, or write, depending on your location, ask them a few questions: Who was buried in the same plot of the person/persons you seek. Who owned the plot. And finally who else is buried in Oak Grove with the same last name.
It is actually better by mail as they have some 32,000 burials there. You can also ask what funeral home was involved. You would be surprised to know how far back some of the Funeral Home records in the area go. Might give a clue to something more.
Also, obituaries can help locate missing links. And the one thing I found particularly useful, was the funeral registers...people who came to view the desceased or to attend the funeral. If you find one for a family member that might have died as late as the past 25 years and they were old, you would be surprised at the names on the list...old friends, sons and daughters of friends, neices and nephews. Many female relatives with their married names. It can be a gold mine....at least it was for me. I was lucky because tucked into it, was the list of people and their addresses who sent flowers or memorials. I located a number of people through this list alone!
Let us know how it goes...have a great day.