In the application of the rule stated in § 1.661(b)-1, the items of deduction which enter into the computation of distributable net income are allocated among the items of income which enter into the computation of distributable net income in accordance with the rules set forth in § 1.652(b)-3, except that, in the absence of specific provisions in the governing instrument, or unless local law requires a different apportionment, amounts paid, permanently set aside, or to be used for the charitable, etc., purposes specified in section 642(c) are first ratably apportioned among each class of items of income entering into the computation of the distributable net income of the estate or trust, in accordance with the rules set out in paragraph (b) of § 1.643(a)-5.