I am not aware of a way to retrofit this type of system to an existing upper, or at least not easily.
Olympic Arms also makes/made (dont see it currently listed on their site) their OA series that also does not require a rear buffer. I never did see them selling parts just for these builds. They made a pistol version and a rifle version.
http://www.olyarms.com/index.php?opt...tpage&Itemid=1
Here is a pic of the OA pistol I had to give you an idea how it works.
