Notes, drafts, bills of exchange, or acceptances issued or drawn by cooperative marketing associations composed of producers of agricultural products shall be deemed to have been issued or drawn for an agricultural purpose, within the meaning of sections 348 and 349 to 352 of this title, if the proceeds thereof have been or are to be advanced by such association to any members thereof for an agricultural purpose, or have been or are to be used by such association in making payments to any members thereof on account of agricultural products delivered by such members to the association, or if such proceeds have been or are to be used by such association to meet expenditures incurred or to be incurred by the association in connection with the grading, processing, packing, preparation for market, or marketing of any agricultural product handled by such association for any of its members: Provided, That the express enumeration in this section of certain classes of paper of cooperative marketing associations as eligible for rediscount shall not be construed as rendering ineligible any other class of paper of such associations which is now eligible for rediscount.