You can use the current navy housing fine, the full auto just will not line up. You do need the 4 position selector lever though.
Past that its just using the right ejector lever in the pack. A 5.56 gun will run with pretty much any spring.
Edit: If you are having Mike do a mp5f sbr for you why not just buy the 4 position housing and have him clip and pin it. The same housing will fit both the 53 and the mp5.