All necessary preliminary expenses actually incurred by the board in the making of surveys, estimates of costs and of revenues, employment of engineers or other employees, the giving of notices, taking of options, and all other expenses of whatsoever nature necessary to be paid prior to the issue, sale and delivery of the revenue bonds herein provided for, may be paid by the board to be reimbursed and repaid out of the proceeds of sale of such revenue bonds in this article provided for.