Why do you register it with an upper? Mine is just a lower, if they come look then I just put that upper on yesterday. My 9mm is registerd as a complete rifle but once I decide on a new lower for it I'll just own two lowers as far as they're concerned.
They want to screw us at every chance they get so I'll screw back, when they make them prohib and come for them they'll get a couple stripped lowers and the rest of the parts are mine till these idiotic Libtards are down the road and the RCMP are hopefully put back in their place.
Not sure what the OP can do, maybe just take a pic of the lower with a tape measure beside it and sent it in, if they want it stripped then tell them you're not a firearms expert and don't know how to take it apart.