Accompanying any ordinance for a local improvement presented by the committee of local improvements to the board shall be a recommendation of such improvement by the committee signed by at least a majority of the members thereof, together with an estimate of the cost of the improvement, including the cost of engineering services, as originally contemplated or as changed, altered or modified at the public hearing, itemized so far as the committee deems necessary and signed by the board’s engineer. The recommendation by the committee shall be prima facie evidence that all the preliminary requirements of the law have been complied with. If a variance is shown on the proceedings in the court, it shall not affect the validity of the proceeding unless the court deems the variance willful and substantial.
     In the event the improvement is to be constructed with assistance from any agency of the federal government or other governmental agency, the estimate of cost shall state this fact and shall set forth the estimated amount that is to be provided by the agency of the federal government or other governmental agency.
     The person appointed to make the assessments as provided hereinafter shall make a true and impartial assessment upon the petitioning district and the property benefited by such improvement of that portion of the estimated cost that is within the benefits exclusive of the amount to be provided by the agency of the federal government or other governmental agency.