Follow the instructions on the order form to the letter or the VA will kick it back to you.
Remember to certify that the graves are unmarked.
It can save a lot of headaches if you can get a descendant to request the stones or get the owner of the cemetery (if it's a family cemetery) to request the stones.
Good luck, and thanks for marking these Southern Patriots' graves! -- Jim Huffman, Gainesville Vols, SCV Camp 373, Pearl River County, MS