I believe your barrel ought to be chrome-lined, as well as the chamber.
As to your second question, first let me say that I am not an expert, nor a lawyer.
My understanding is that a lower that was mfd pre-ban MUST have been ASSEMBLED as a complete rifle in order to legally mount an upper with pre-ban features.
IOW, suppose you had a lower that was definitely mfd pre-ban. In a worst-case scenario, you would be asked to PROVE in court that it had been assembled to an upper with pre-ban features PRIOR to the ban. This is a case of guilty until proven innocent, and has happened.
Lots of folks have been stuck with pre-ban lowers that they cannot document as having been assembled into pre-ban configuration rifles prior to the ban.
I strongly suggest you confirm my statements by going to the Legal Forum on this site, and asking the legal eagles there. Good luck.