Unity 3D - Shuffle voxel cubes in a game object

I am trying take a group of voxel ground cubes and have them shuffled or randomly placed differing from how they are placed on the game area. I am attempting to make it where the grass is not in a pattern and has more of a visual appeal. I have tried several solutions I have found and none quite fit the bill, I even tried one that was suppose to take multiple cubes and fill the space defined in the object group. That failed miserably with more than undesirable effects. I have read a few other posts that are similar in nature but not the same of what I am after. Simply put I want to take a group of prefabs and replace all the blocks in an object group randomly with the blocks provided to the script. I am even open to creating a cube to define the space that is to be filled. Keep in mind I am not new to programming, however I am new to Unity Game Development, so keep that in mind. I used the following from a post however it only allows for 1 prefab and it does not conform to the areas that the ground tiles are placed in the object group.

Thanks folks!