The state board may exempt from any schedule of installation adopted pursuant to Section 43654 or 43655:
- (a) Motor vehicles or classifications or subclassifications of motor vehicles for which certified devices are not available.
- (b) Motor vehicles or classifications or subclassifications of motor vehicles whose emissions are found by appropriate tests to meet applicable emission standards without an additional motor vehicle pollution control device.
- (c) Implements of husbandry.
- (d) Vehicles which qualify for special identification plates pursuant to Section 5004 of the Vehicle Code.