You did not get screwed. #1. The barrel diameter is .750 at the muzzle, Bushy makes two different Dissapator barrels, a lightweight thin profile, and a heavy profile. You obviously have the heavy profile, which most would consider preferable to the lightweight barrel. I am not sure of the diameter under the handguards, I believe it is .840" #2. Threading the end of the barrel is illegal and will get you 10 years in prison unless the AWB sunsets on Sept. 13 I don't think a threaded barrel really suffers any performance decrease on a 16" bbl. A good gunsmith can thread it, but I would just leave it alone. #3 Yes, you can remove the Front Sight Base and replace it with a pre-ban one (again illegal), but do you really need a bayonet, I would invest in a pistol as a backup weapon. #4 Yes, you can attach this upper to any mil-spec lower receiver and it should work just fine. If you are planning on attaching this upper onto a pre-ban lower, your modifications will be legal, but research your local and Federal laws before doing it. You can go to Bushy's web site and see their offerings to give you a better idea of what you can do and prices.