Where work to be performed, which would otherwise be subject to the State Contract Act, does not lend itself to the preparation of plans and specifications to enable bids to be taken on a lump sum or unit basis, the department may perform such work by the use of rented tools or equipment, either with operators furnished or unoperated. Contracts for such rentals shall not be subject to the State Contract Act, but shall be subject to all of the provisions of Section 136.5 of the Streets and Highways Code.