Is this true for every state? The reason I gave my answer as I did, was because the OP wanted to know about registration. There is no such thing for an unserialized firearm.
Building a rifle from an 80% lower still has to have approval from the BATFE, when you've done your paperwork correctly and gotten approval, your rifle is then effectively registered once it meets BATFE requirements as far as being serialized and all that.
Tomorrow (Saturday, 7/24/13) anti-gun idiots all over the US are planning to abandon the Starbucks franchise for a single day to make a point about their decision to allow customers open and concealed carry on their property in permitting states:
Link
If you enjoy coffey or anything Starbucks carries, you can show your appreciation for their stance by joining myself and other gun owners across the nation by walking into your local Starbucks and buying yourself something you'll enjoy. Be sure to let them know at the counter that you appreciate their stance and are acting accordingly. Nothing could make me happier than Starbucks having a record income spike on 7/24/13.
The only thick skin you'll be needing is whatever animal hide your wallet is made of.... If it's not thicker than Tom's own hide, you are screwed...
Come to think of it, you're probably screwed anyways, but we let the new guys enjoy a false sense of hope for a brief period....
The Wild Man (Tom) has probably done it. That dude is hardcore, and has some hilarious stories involving riding. Stick around a bit, and you'll probably hear a story that involves the partial consumption of a dune, I swear it.
Relocation sucks in the moment, but I think in the long run they'll be happier down here. I stipulate that they further deserve a good severe beating in addition to being fired from "public service".
On the thicker barrels it doesn't really matter so much, but there are some experts who feel that an overtorqued set-screw type can affect accuracy... That's FWIW and YMMV...
I think all the suggestions so far are great. I would suggest that standalone systems would also sell well, like a gas system, BCG as a whole, LPKs, and such-like. Things that can by themselves bring a whole build together.
Adjustable GB can keep you from experiencing overgassing at the user end. May not be a problem at all, but you might stumble upon a particular load that sends lots of nice smelly gas out of your ejection port on every shot.....