A grant under section 3335 of this title shall not exceed (1) 20 per centum of the cost of the project for which the grant is made; nor (2) the Federal grant made with respect to the project under the legislation referred to in paragraph (2) of section 3338 of this title. In no case shall the total Federal contributions to the cost of such project be more than 80 per centum. Notwithstanding any other provision of law, including requirements with respect to non-Federal contributions, grants under section 3335 of this title shall be eligible for inclusion (directly or through refunds or credits) as part of the financing for such projects: Provided, That proj­ects or activities on the basis of which assistance is provided under section 3305(c) of this title shall not be eligible for assistance under section 3335 of this title.