All though the m203 combo wasn't a standard thing in the nam era, they did have them. Unfortuantely they mostly all came with the heat shield "scarface" grip. You can get them with the barrel mounts only, but you would still have to remove the bottom of the triangle heat shield. I don't know and wouldn't trust mounting a rail to the bottom of the shield, as it would look pretty funky, and also, depending on the quality of the piece, might cause a serious break in the hand guard. I think the scar face heat shield and 203 looks bad assed though....