Notwithstanding the model years for which clean-fuel vehicle standards are applicable as provided in section
7583 of this title, for purposes of this section, light duty trucks of up to 6,000 lbs. GVWR and light-duty vehicles manufactured in model years 1998 through model year 2000 shall be treated as clean-fuel vehicles only if such vehicles comply with the standards applicable under section
7583 of this title for vehicles in the same class for the model year 2001. The requirements of subsection (b) of this section shall take effect on the earlier of the following:
Whenever the effective date of subsection (b) of this section is delayed pursuant to paragraph (1) of this subsection, the phase-in schedule under subsection (b) of this section shall be modified to commence with the model year referred to in paragraph (1) in lieu of model year 1998.