Nicely said buddy. I would figure the PDI would be the same setup in a sense and any houpup will work since its mostly a inner barrel and bucking mod.Anybarrel with a hopup window cut into it accepts the r-hop. Just make sure the hopup arms have a flat nub as long as the r-hop itself. It will work with the normal nub but not as well. I'm not sure how to mod the pdi units as I have no experience with those though.