"RR" and "Lighting Link" are 2 terms that do not go together. Two completly differant items.
A "RR" Registered Receiver is a Receiver that has a sear hole drilled in it and the Lower it self is the Machine Gun.
A "Lighting Link" is a Conversion Device, the Device is the regestered part, that is why you can move it from gun to gun.
I am not aware of any Lighting Links that are married to a specific Lower Receiver so I do not see how you could have a Registered Receiver Lightning Link.