Here is the law
(r)It shall be unlawful for any person to assemble from imported parts any semiautomatic rifle or any shotgun which is identical to any rifle or shotgun prohibited from importation under section 925(d)(3) of this chapter as not being particularly suitable for or readily adaptable to sporting purposes except that this subsection shall not apply to—
the assembly of any such rifle or shotgun for sale or distribution by a licensed manufacturer to the United States or any department or agency thereof or to any State or any department, agency, or political subdivision thereof; or
the assembly of any such rifle or shotgun for the purposes of testing or experimentation authorized by the Attorney General.
I am not aware of an official ATF parts count determination for the Super Nova, however someone on another shotgun forum was advised in writing by the ATF that since the NOVA's stock and receiver is one piece, only two parts would have to be replaced in order to increase capacity. For your Super Nova you probably would need to replace 3.