It would really help to know what rail setup and stock mounting options you have. A simple picture would do well, or a picture of one similar. Do you have any rail options on the handguard? Front sight base or gas block? Do you have the M4 collapsable stock or another option? All of these things will affect your options.
ΜΟΛΩΝ ΛΑΒΕ- Greek:"Come and take them..." Meaning: Here we peaceably stand as armed and free men, willing to defend that peace, and ready to make war upon anyone who threatens that freedom.