In applying as the Guam Territorial income tax the income-tax laws in force in Guam pursuant to subsection (a) of this section, the rate of tax under sections 871, 881, 884, 1441, 1442, 1443, 1445, and 1446 of the Internal Revenue Code of 1986 [
26 U.S.C. 871, 881, 884, 1441, 1442, 1443, 1445, and 1446] on any item of income from sources within Guam shall be the same as the rate which would apply with respect to such item were Guam treated as part of the United States for purposes of the treaty obligations of the United States. The preceding sentence shall not apply to determine the rate of tax on any item of income received from a Guam payor if, for any taxable year, the taxes of the Guam payor were rebated under Guam law. For purposes of this subsection, the term “Guam payor” means the person from whom the item of income would be deemed to be received for purposes of claiming treaty benefits were Guam treated as part of the United States.