The commissioners appointed pursuant to Article 1 of this chapter shall assess the costs of the project, or in the event the board has divided the project into units of construction, the cost of the unit or units specified for immediate construction, upon the benefited land. In the event that the costs of the project are to be paid in part from the proceeds of a loan from the United States, the portion to be so paid may be separately assessed in the manner provided in Section 44031, and the portion of the costs of the project to be paid from other funds shall be assessed as provided in this chapter.