Even on the Eagle RRV, the backplate carrier isn't directly integrated: the fastex buckles on the rear plate attach to adapter straps which are fastened to the PALS strips on the RRV's shoulder pads.
This is the only semi-clear picture I could find to illustrate it:
On the right picture, see how the two loose male fastex clips are part of straps which are attached to the bottom strip on the shoulder pads?
So you just need the backplate carrier and straps with the same type of buckles (beware PANTAC's backplate uses the newer buckles, which aren't compatible with the old ones). The straps are just loops with snaps.