Notwithstanding any other provision of law, in any county employing a competent engineer as road commissioner, the board of supervisors may elect to perform work or projects or let contracts for the performance of work or projects under the provisions of the State Contract Act pursuant to Chapter 1 (commencing with Section 10100) of Part 2 of Division 2 of the Public Contract Code; and when such election is made, references in said act to state shall mean county, and references to any state agency shall mean county board of supervisors, or such county agency as the board of supervisors may designate, and the provisions of said act shall be fully applicable to work or projects so to be performed by the county.