Okay for anything that happened under Andrew Johnson, remember you need living parties that have a dispute over the legal rights. The legal issue is whether any rights given under statute during Reconstruction are assignable (can they be passed to heirs)--the answer depends on what the statute says. If the statute says nothings, the courts will interpret it based on Congressional intent. So ignoring things like statute of limitations or whether there is a statute giving them the power to sue the gov't, its possible living parties could have legal rights in dispute...
Just to reemphasize a point, say the government in 1866 emphasized that each ex-slave was entitled to 100 bucks and the this right was assignable to the ex-slave heirs if the ex-slave died before receiving the money. Now you get to today, all the heirs of the ex slaves would be entitled to a portion of that 100 bucks, if there were 100 of them, then each would be entitled to a dollar under the statute. This would not be reparations which was my first point, theortically its possible African Americans who can prove their heritage would be entitled to any benefits their ancestors were granted, that are assignable, but that is all they are entitled to.